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<HTML> <HTML>
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<TITLE>User's Guide to gperf - Introduction</TITLE> <TITLE>Perfect Hash Function Generator - GNU GENERAL PUBLIC LICENSE</TITLE>
</HEAD> </HEAD>
<BODY> <BODY>
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<P><HR><P> <P><HR><P>
<H1><A NAME="SEC1" HREF="gperf_toc.html#TOC1">Introduction</A></H1> <H1><A NAME="SEC1" HREF="gperf_toc.html#TOC1">GNU GENERAL PUBLIC LICENSE</A></H1>
<P> <P>
This manual documents the GNU <CODE>gperf</CODE> perfect hash function generator Version 2, June 1991
utility, focusing on its features and how to use them, and how to report
bugs.
</P> </P>
<PRE>
Copyright (C) 1989, 1991 Free Software Foundation, Inc.,
59 Temple Place, Suite 330, Boston, MA 02111-1307, USA.
Everyone is permitted to copy and distribute verbatim copies
of this license document, but changing it is not allowed.
</PRE>
<H2><A NAME="SEC2" HREF="gperf_toc.html#TOC2">Preamble</A></H2>
<P>
The licenses for most software are designed to take away your
freedom to share and change it. By contrast, the GNU General Public
License is intended to guarantee your freedom to share and change free
software--to make sure the software is free for all its users. This
General Public License applies to most of the Free Software
Foundation's software and to any other program whose authors commit to
using it. (Some other Free Software Foundation software is covered by
the GNU Library General Public License instead.) You can apply it to
your programs, too.
</P>
<P>
When we speak of free software, we are referring to freedom, not
price. Our General Public Licenses are designed to make sure that you
have the freedom to distribute copies of free software (and charge for
this service if you wish), that you receive source code or can get it
if you want it, that you can change the software or use pieces of it
in new free programs; and that you know you can do these things.
</P>
<P>
To protect your rights, we need to make restrictions that forbid
anyone to deny you these rights or to ask you to surrender the rights.
These restrictions translate to certain responsibilities for you if you
distribute copies of the software, or if you modify it.
</P>
<P>
For example, if you distribute copies of such a program, whether
gratis or for a fee, you must give the recipients all the rights that
you have. You must make sure that they, too, receive or can get the
source code. And you must show them these terms so they know their
rights.
</P>
<P>
We protect your rights with two steps: (1) copyright the software, and
(2) offer you this license which gives you legal permission to copy,
distribute and/or modify the software.
</P>
<P>
Also, for each author's protection and ours, we want to make certain
that everyone understands that there is no warranty for this free
software. If the software is modified by someone else and passed on, we
want its recipients to know that what they have is not the original, so
that any problems introduced by others will not reflect on the original
authors' reputations.
</P>
<P>
Finally, any free program is threatened constantly by software
patents. We wish to avoid the danger that redistributors of a free
program will individually obtain patent licenses, in effect making the
program proprietary. To prevent this, we have made it clear that any
patent must be licensed for everyone's free use or not licensed at all.
</P>
<P>
The precise terms and conditions for copying, distribution and
modification follow.
</P>
<P>
TERMS AND CONDITIONS FOR COPYING, DISTRIBUTION AND MODIFICATION
</P>
<OL>
<LI>
This License applies to any program or other work which contains
a notice placed by the copyright holder saying it may be distributed
under the terms of this General Public License. The "Program", below,
refers to any such program or work, and a "work based on the Program"
means either the Program or any derivative work under copyright law:
that is to say, a work containing the Program or a portion of it,
either verbatim or with modifications and/or translated into another
language. (Hereinafter, translation is included without limitation in
the term "modification".) Each licensee is addressed as "you".
Activities other than copying, distribution and modification are not
covered by this License; they are outside its scope. The act of
running the Program is not restricted, and the output from the Program
is covered only if its contents constitute a work based on the
Program (independent of having been made by running the Program).
Whether that is true depends on what the Program does.
<LI>
You may copy and distribute verbatim copies of the Program's
source code as you receive it, in any medium, provided that you
conspicuously and appropriately publish on each copy an appropriate
copyright notice and disclaimer of warranty; keep intact all the
notices that refer to this License and to the absence of any warranty;
and give any other recipients of the Program a copy of this License
along with the Program.
You may charge a fee for the physical act of transferring a copy, and
you may at your option offer warranty protection in exchange for a fee.
<LI>
You may modify your copy or copies of the Program or any portion
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distribute such modifications or work under the terms of Section 1
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<OL>
<LI>
You must cause the modified files to carry prominent notices
stating that you changed the files and the date of any change.
<LI>
You must cause any work that you distribute or publish, that in
whole or in part contains or is derived from the Program or any
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<LI>
If the modified program normally reads commands interactively
when run, you must cause it, when started running for such
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the Program is not required to print an announcement.)
</OL>
These requirements apply to the modified work as a whole. If
identifiable sections of that work are not derived from the Program,
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the scope of this License.
<LI>
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under Section 2) in object code or executable form under the terms of
Sections 1 and 2 above provided that you also do one of the following:
<OL>
<LI>
Accompany it with the complete corresponding machine-readable
source code, which must be distributed under the terms of Sections
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<LI>
Accompany it with a written offer, valid for at least three
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</OL>
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<LI>
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<LI>
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distribute the Program or its derivative works. These actions are
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modifying or distributing the Program (or any work based on the
Program), you indicate your acceptance of this License to do so, and
all its terms and conditions for copying, distributing or modifying
the Program or works based on it.
<LI>
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<LI>
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conditions are imposed on you (whether by court order, agreement or
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License and any other pertinent obligations, then as a consequence you
may not distribute the Program at all. For example, if a patent
license would not permit royalty-free redistribution of the Program by
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This section is intended to make thoroughly clear what is believed to
be a consequence of the rest of this License.
<LI>
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certain countries either by patents or by copyrighted interfaces, the
original copyright holder who places the Program under this License
may add an explicit geographical distribution limitation excluding
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<LI>
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later version", you have the option of following the terms and conditions
either of that version or of any later version published by the Free
Software Foundation. If the Program does not specify a version number of
this License, you may choose any version ever published by the Free Software
Foundation.
<LI>
If you wish to incorporate parts of the Program into other free
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to ask for permission. For software which is copyrighted by the Free
Software Foundation, write to the Free Software Foundation; we sometimes
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NO WARRANTY
<LI>
BECAUSE THE PROGRAM IS LICENSED FREE OF CHARGE, THERE IS NO WARRANTY
FOR THE PROGRAM, TO THE EXTENT PERMITTED BY APPLICABLE LAW. EXCEPT WHEN
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PROVIDE THE PROGRAM "AS IS" WITHOUT WARRANTY OF ANY KIND, EITHER EXPRESSED
OR IMPLIED, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES OF
MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE. THE ENTIRE RISK AS
TO THE QUALITY AND PERFORMANCE OF THE PROGRAM IS WITH YOU. SHOULD THE
PROGRAM PROVE DEFECTIVE, YOU ASSUME THE COST OF ALL NECESSARY SERVICING,
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<LI>
IN NO EVENT UNLESS REQUIRED BY APPLICABLE LAW OR AGREED TO IN WRITING
WILL ANY COPYRIGHT HOLDER, OR ANY OTHER PARTY WHO MAY MODIFY AND/OR
REDISTRIBUTE THE PROGRAM AS PERMITTED ABOVE, BE LIABLE TO YOU FOR DAMAGES,
INCLUDING ANY GENERAL, SPECIAL, INCIDENTAL OR CONSEQUENTIAL DAMAGES ARISING
OUT OF THE USE OR INABILITY TO USE THE PROGRAM (INCLUDING BUT NOT LIMITED
TO LOSS OF DATA OR DATA BEING RENDERED INACCURATE OR LOSSES SUSTAINED BY
YOU OR THIRD PARTIES OR A FAILURE OF THE PROGRAM TO OPERATE WITH ANY OTHER
PROGRAMS), EVEN IF SUCH HOLDER OR OTHER PARTY HAS BEEN ADVISED OF THE
POSSIBILITY OF SUCH DAMAGES.
</OL>
<P>
END OF TERMS AND CONDITIONS
</P>
<H2><A NAME="SEC3" HREF="gperf_toc.html#TOC3">How to Apply These Terms to Your New Programs</A></H2>
<P>
If you develop a new program, and you want it to be of the greatest
possible use to the public, the best way to achieve this is to make it
free software which everyone can redistribute and change under these terms.
</P>
<P>
To do so, attach the following notices to the program. It is safest
to attach them to the start of each source file to most effectively
convey the exclusion of warranty; and each file should have at least
the "copyright" line and a pointer to where the full notice is found.
</P>
<PRE>
<VAR>one line to give the program's name and an idea of what it does.</VAR>
Copyright (C) <VAR>year</VAR> <VAR>name of author</VAR>
This program is free software; you can redistribute it and/or
modify it under the terms of the GNU General Public License
as published by the Free Software Foundation; either version 2
of the License, or (at your option) any later version.
This program is distributed in the hope that it will be useful,
but WITHOUT ANY WARRANTY; without even the implied warranty of
MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
GNU General Public License for more details.
You should have received a copy of the GNU General Public License
along with this program; if not, write to the Free Software
Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA 02111-1307, USA.
</PRE>
<P>
Also add information on how to contact you by electronic and paper mail.
</P>
<P>
If the program is interactive, make it output a short notice like this
when it starts in an interactive mode:
</P>
<PRE>
Gnomovision version 69, Copyright (C) <VAR>year</VAR> <VAR>name of author</VAR>
Gnomovision comes with ABSOLUTELY NO WARRANTY; for details
type `show w'. This is free software, and you are welcome
to redistribute it under certain conditions; type `show c'
for details.
</PRE>
<P>
The hypothetical commands <SAMP>`show w'</SAMP> and <SAMP>`show c'</SAMP> should show
the appropriate parts of the General Public License. Of course, the
commands you use may be called something other than <SAMP>`show w'</SAMP> and
<SAMP>`show c'</SAMP>; they could even be mouse-clicks or menu items--whatever
suits your program.
</P>
<P>
You should also get your employer (if you work as a programmer) or your
school, if any, to sign a "copyright disclaimer" for the program, if
necessary. Here is a sample; alter the names:
</P>
<PRE>
Yoyodyne, Inc., hereby disclaims all copyright
interest in the program `Gnomovision'
(which makes passes at compilers) written
by James Hacker.
<VAR>signature of Ty Coon</VAR>, 1 April 1989
Ty Coon, President of Vice
</PRE>
<P>
This General Public License does not permit incorporating your program into
proprietary programs. If your program is a subroutine library, you may
consider it more useful to permit linking proprietary applications with the
library. If this is what you want to do, use the GNU Library General
Public License instead of this License.
</P>
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<TITLE>User's Guide to gperf - 7 Implementation Details of GNU gperf</TITLE> <TITLE>Perfect Hash Function Generator - 8 Bibliography</TITLE>
</HEAD> </HEAD>
<BODY> <BODY>
Go to the <A HREF="gperf_1.html">first</A>, <A HREF="gperf_9.html">previous</A>, <A HREF="gperf_11.html">next</A>, <A HREF="gperf_11.html">last</A> section, <A HREF="gperf_toc.html">table of contents</A>. Go to the <A HREF="gperf_1.html">first</A>, <A HREF="gperf_9.html">previous</A>, <A HREF="gperf_11.html">next</A>, <A HREF="gperf_11.html">last</A> section, <A HREF="gperf_toc.html">table of contents</A>.
<P><HR><P> <P><HR><P>
<H1><A NAME="SEC22" HREF="gperf_toc.html#TOC22">7 Implementation Details of GNU <CODE>gperf</CODE></A></H1> <H1><A NAME="SEC23" HREF="gperf_toc.html#TOC23">8 Bibliography</A></H1>
<P> <P>
A paper describing the high-level description of the data structures and [1] Chang, C.C.: <I>A Scheme for Constructing Ordered Minimal Perfect
algorithms used to implement <CODE>gperf</CODE> will soon be available. This Hashing Functions</I> Information Sciences 39(1986), 187-195.
paper is useful not only from a maintenance and enhancement perspective,
but also because they demonstrate several clever and useful programming [2] Cichelli, Richard J. <I>Author's Response to "On Cichelli's Minimal Perfect Hash
techniques, e.g., `Iteration Number' boolean arrays, double Functions Method"</I> Communications of the ACM, 23, 12(December 1980), 729.
hashing, a "safe" and efficient method for reading arbitrarily long
input from a file, and a provably optimal algorithm for simultaneously [3] Cichelli, Richard J. <I>Minimal Perfect Hash Functions Made Simple</I>
determining both the minimum and maximum elements in a list. Communications of the ACM, 23, 1(January 1980), 17-19.
[4] Cook, C. R. and Oldehoeft, R.R. <I>A Letter Oriented Minimal
Perfect Hashing Function</I> SIGPLAN Notices, 17, 9(September 1982), 18-27.
</P> </P>
<P>
[5] Cormack, G. V. and Horspool, R. N. S. and Kaiserwerth, M.
<I>Practical Perfect Hashing</I> Computer Journal, 28, 1(January 1985), 54-58.
[6] Jaeschke, G. <I>Reciprocal Hashing: A Method for Generating Minimal
Perfect Hashing Functions</I> Communications of the ACM, 24, 12(December
1981), 829-833.
</P>
<P>
[7] Jaeschke, G. and Osterburg, G. <I>On Cichelli's Minimal Perfect
Hash Functions Method</I> Communications of the ACM, 23, 12(December 1980),
728-729.
</P>
<P>
[8] Sager, Thomas J. <I>A Polynomial Time Generator for Minimal Perfect
Hash Functions</I> Communications of the ACM, 28, 5(December 1985), 523-532
</P>
<P>
[9] Schmidt, Douglas C. <I>GPERF: A Perfect Hash Function Generator</I>
Second USENIX C++ Conference Proceedings, April 1990.
</P>
<P>
[10] Sebesta, R.W. and Taylor, M.A. <I>Minimal Perfect Hash Functions
for Reserved Word Lists</I> SIGPLAN Notices, 20, 12(September 1985), 47-53.
</P>
<P>
[11] Sprugnoli, R. <I>Perfect Hashing Functions: A Single Probe
Retrieving Method for Static Sets</I> Communications of the ACM, 20
11(November 1977), 841-850.
</P>
<P>
[12] Stallman, Richard M. <I>Using and Porting GNU CC</I> Free Software Foundation,
1988.
</P>
<P>
[13] Stroustrup, Bjarne <I>The C++ Programming Language.</I> Addison-Wesley, 1986.
</P>
<P>
[14] Tiemann, Michael D. <I>User's Guide to GNU C++</I> Free Software
Foundation, 1989.
</P>
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Go to the <A HREF="gperf_1.html">first</A>, <A HREF="gperf_9.html">previous</A>, <A HREF="gperf_11.html">next</A>, <A HREF="gperf_11.html">last</A> section, <A HREF="gperf_toc.html">table of contents</A>. Go to the <A HREF="gperf_1.html">first</A>, <A HREF="gperf_9.html">previous</A>, <A HREF="gperf_11.html">next</A>, <A HREF="gperf_11.html">last</A> section, <A HREF="gperf_toc.html">table of contents</A>.
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<H1><A NAME="SEC23" HREF="gperf_toc.html#TOC23">8 Bibliography</A></H1> <H1><A NAME="SEC24" HREF="gperf_toc.html#TOC24">Concept Index</A></H1>
<P> <P>
[1] Chang, C.C.: <I>A Scheme for Constructing Ordered Minimal Perfect <H2>%</H2>
Hashing Functions</I> Information Sciences 39(1986), 187-195. <DIR>
<LI><A HREF="gperf_5.html#IDX8"><SAMP>`%%'</SAMP></A>
[2] Cichelli, Richard J. <I>Author's Response to "On Cichelli's Minimal Perfect Hash <LI><A HREF="gperf_5.html#IDX9"><SAMP>`%{'</SAMP></A>
Functions Method"</I> Communications of the ACM, 23, 12(December 1980), 729. <LI><A HREF="gperf_5.html#IDX10"><SAMP>`%}'</SAMP></A>
</DIR>
[3] Cichelli, Richard J. <I>Minimal Perfect Hash Functions Made Simple</I> <H2>a</H2>
Communications of the ACM, 23, 1(January 1980), 17-19. <DIR>
<LI><A HREF="gperf_6.html#IDX20">Array name</A>
[4] Cook, C. R. and Oldehoeft, R.R. <I>A Letter Oriented Minimal </DIR>
Perfect Hashing Function</I> SIGPLAN Notices, 17, 9(September 1982), 18-27. <H2>b</H2>
<DIR>
</P> <LI><A HREF="gperf_2.html#IDX1">Bugs</A>
<P> </DIR>
[5] Cormack, G. V. and Horspool, R. N. S. and Kaiserwerth, M. <H2>c</H2>
<I>Practical Perfect Hashing</I> Computer Journal, 28, 1(January 1985), 54-58. <DIR>
<LI><A HREF="gperf_6.html#IDX19">Class name</A>
[6] Jaeschke, G. <I>Reciprocal Hashing: A Method for Generating Minimal </DIR>
Perfect Hashing Functions</I> Communications of the ACM, 24, 12(December <H2>d</H2>
1981), 829-833. <DIR>
<LI><A HREF="gperf_5.html#IDX5">Declaration section</A>
</P> <LI><A HREF="gperf_6.html#IDX16">Delimiters</A>
<P> <LI><A HREF="gperf_6.html#IDX22">Duplicates</A>
[7] Jaeschke, G. and Osterburg, G. <I>On Cichelli's Minimal Perfect </DIR>
Hash Functions Method</I> Communications of the ACM, 23, 12(December 1980), <H2>f</H2>
728-729. <DIR>
<LI><A HREF="gperf_5.html#IDX4">Format</A>
</P> <LI><A HREF="gperf_5.html#IDX7">Functions section</A>
<P> </DIR>
[8] Sager, Thomas J. <I>A Polynomial Time Generator for Minimal Perfect <H2>h</H2>
Hash Functions</I> Communications of the ACM, 28, 5(December 1985), 523-532 <DIR>
<LI><A HREF="gperf_5.html#IDX12">hash</A>
</P> <LI><A HREF="gperf_5.html#IDX11">hash table</A>
<P> </DIR>
[9] Schmidt, Douglas C. <I>GPERF: A Perfect Hash Function Generator</I> <H2>i</H2>
Second USENIX C++ Conference Proceedings, April 1990. <DIR>
<LI><A HREF="gperf_5.html#IDX13">in_word_set</A>
</P> <LI><A HREF="gperf_6.html#IDX18">Initializers</A>
<P> </DIR>
[10] Sebesta, R.W. and Taylor, M.A. <I>Minimal Perfect Hash Functions <H2>j</H2>
for Reserved Word Lists</I> SIGPLAN Notices, 20, 12(September 1985), 47-53. <DIR>
<LI><A HREF="gperf_6.html#IDX23">Jump value</A>
</P> </DIR>
<P> <H2>k</H2>
[11] Sprugnoli, R. <I>Perfect Hashing Functions: A Single Probe <DIR>
Retrieving Method for Static Sets</I> Communications of the ACM, 20 <LI><A HREF="gperf_5.html#IDX6">Keywords section</A>
11(November 1977), 841-850. </DIR>
<H2>m</H2>
</P> <DIR>
<P> <LI><A HREF="gperf_4.html#IDX3">Minimal perfect hash functions</A>
[12] Stallman, Richard M. <I>Using and Porting GNU CC</I> Free Software Foundation, </DIR>
1988. <H2>n</H2>
<DIR>
</P> <LI><A HREF="gperf_5.html#IDX15">NUL</A>
<P> </DIR>
[13] Stroustrup, Bjarne <I>The C++ Programming Language.</I> Addison-Wesley, 1986. <H2>s</H2>
<DIR>
</P> <LI><A HREF="gperf_6.html#IDX17">Slot name</A>
<P> <LI><A HREF="gperf_4.html#IDX2">Static search structure</A>
[14] Tiemann, Michael D. <I>User's Guide to GNU C++</I> Free Software <LI><A HREF="gperf_5.html#IDX14"><CODE>switch</CODE></A>, <A HREF="gperf_6.html#IDX21"><CODE>switch</CODE></A>
Foundation, 1989. </DIR>
</P> </P>
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</HEAD> </HEAD>
<BODY> <BODY>
Go to the <A HREF="gperf_1.html">first</A>, <A HREF="gperf_1.html">previous</A>, <A HREF="gperf_3.html">next</A>, <A HREF="gperf_11.html">last</A> section, <A HREF="gperf_toc.html">table of contents</A>. Go to the <A HREF="gperf_1.html">first</A>, <A HREF="gperf_1.html">previous</A>, <A HREF="gperf_3.html">next</A>, <A HREF="gperf_11.html">last</A> section, <A HREF="gperf_toc.html">table of contents</A>.
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<H1><A NAME="SEC2" HREF="gperf_toc.html#TOC2">GNU GENERAL PUBLIC LICENSE</A></H1> <H1><A NAME="SEC4" HREF="gperf_toc.html#TOC4">Contributors to GNU <CODE>gperf</CODE> Utility</A></H1>
<P>
Version 1, February 1989
</P>
<PRE>
Copyright (C) 1989 Free Software Foundation, Inc.
675 Mass Ave, Cambridge, MA 02139, USA
Everyone is permitted to copy and distribute verbatim copies
of this license document, but changing it is not allowed.
</PRE>
<H2><A NAME="SEC3" HREF="gperf_toc.html#TOC3">Preamble</A></H2>
<P>
The license agreements of most software companies try to keep users
at the mercy of those companies. By contrast, our General Public
License is intended to guarantee your freedom to share and change free
software--to make sure the software is free for all its users. The
General Public License applies to the Free Software Foundation's
software and to any other program whose authors commit to using it.
You can use it for your programs, too.
</P>
<P>
When we speak of free software, we are referring to freedom, not
price. Specifically, the General Public License is designed to make
sure that you have the freedom to give away or sell copies of free
software, that you receive source code or can get it if you want it,
that you can change the software or use pieces of it in new free
programs; and that you know you can do these things.
</P>
<P>
To protect your rights, we need to make restrictions that forbid
anyone to deny you these rights or to ask you to surrender the rights.
These restrictions translate to certain responsibilities for you if you
distribute copies of the software, or if you modify it.
</P>
<P>
For example, if you distribute copies of a such a program, whether
gratis or for a fee, you must give the recipients all the rights that
you have. You must make sure that they, too, receive or can get the
source code. And you must tell them their rights.
</P>
<P>
We protect your rights with two steps: (1) copyright the software, and
(2) offer you this license which gives you legal permission to copy,
distribute and/or modify the software.
</P>
<P>
Also, for each author's protection and ours, we want to make certain
that everyone understands that there is no warranty for this free
software. If the software is modified by someone else and passed on, we
want its recipients to know that what they have is not the original, so
that any problems introduced by others will not reflect on the original
authors' reputations.
</P>
<P>
The precise terms and conditions for copying, distribution and
modification follow.
</P>
<P>
TERMS AND CONDITIONS
</P>
<OL>
<LI>
This License Agreement applies to any program or other work which
contains a notice placed by the copyright holder saying it may be
distributed under the terms of this General Public License. The
"Program", below, refers to any such program or work, and a "work based
on the Program" means either the Program or any work containing the
Program or a portion of it, either verbatim or with modifications. Each
licensee is addressed as "you".
<LI>
You may copy and distribute verbatim copies of the Program's source
code as you receive it, in any medium, provided that you conspicuously and
appropriately publish on each copy an appropriate copyright notice and
disclaimer of warranty; keep intact all the notices that refer to this
General Public License and to the absence of any warranty; and give any
other recipients of the Program a copy of this General Public License
along with the Program. You may charge a fee for the physical act of
transferring a copy.
<LI>
You may modify your copy or copies of the Program or any portion of
it, and copy and distribute such modifications under the terms of Paragraph
1 above, provided that you also do the following:
<UL> <UL>
<LI> <LI>
cause the modified files to carry prominent notices stating that <A NAME="IDX1"></A>
you changed the files and the date of any change; and The GNU <CODE>gperf</CODE> perfect hash function generator utility was
originally written in GNU C++ by Douglas C. Schmidt. It is now also
available in a highly-portable "old-style" C version. The general
idea for the perfect hash function generator was inspired by Keith
Bostic's algorithm written in C, and distributed to net.sources around
1984. The current program is a heavily modified, enhanced, and extended
implementation of Keith's basic idea, created at the University of
California, Irvine. Bugs, patches, and suggestions should be reported
to <CODE>&#60;bug-gnu-utils@gnu.org&#62;</CODE>.
<LI> <LI>
cause the whole of any work that you distribute or publish, that Special thanks is extended to Michael Tiemann and Doug Lea, for
in whole or in part contains the Program or any part thereof, either providing a useful compiler, and for giving me a forum to exhibit my
with or without modifications, to be licensed at no charge to all creation.
third parties under the terms of this General Public License (except
that you may choose to grant warranty protection to some or all In addition, Adam de Boor and Nels Olson provided many tips and insights
third parties, at your option). that greatly helped improve the quality and functionality of <CODE>gperf</CODE>.
<LI> <LI>
If the modified program normally reads commands interactively when A testsuite was added by Bruno Haible. He also rewrote the output
run, you must cause it, when started running for such interactive use routines for better reliability.
in the simplest and most usual way, to print or display an
announcement including an appropriate copyright notice and a notice
that there is no warranty (or else, saying that you provide a
warranty) and that users may redistribute the program under these
conditions, and telling the user how to view a copy of this General
Public License.
<LI>
You may charge a fee for the physical act of transferring a
copy, and you may at your option offer warranty protection in
exchange for a fee.
</UL> </UL>
Mere aggregation of another independent work with the Program (or its
derivative) on a volume of a storage or distribution medium does not bring
the other work under the scope of these terms.
<LI>
You may copy and distribute the Program (or a portion or derivative of
it, under Paragraph 2) in object code or executable form under the terms of
Paragraphs 1 and 2 above provided that you also do one of the following:
<UL>
<LI>
accompany it with the complete corresponding machine-readable
source code, which must be distributed under the terms of
Paragraphs 1 and 2 above; or,
<LI>
accompany it with a written offer, valid for at least three
years, to give any third party free (except for a nominal charge
for the cost of distribution) a complete machine-readable copy of the
corresponding source code, to be distributed under the terms of
Paragraphs 1 and 2 above; or,
<LI>
accompany it with the information you received as to where the
corresponding source code may be obtained. (This alternative is
allowed only for noncommercial distribution and only if you
received the program in object code or executable form alone.)
</UL>
Source code for a work means the preferred form of the work for making
modifications to it. For an executable file, complete source code means
all the source code for all modules it contains; but, as a special
exception, it need not include source code for modules which are standard
libraries that accompany the operating system on which the executable
file runs, or for standard header files or definitions files that
accompany that operating system.
<LI>
You may not copy, modify, sublicense, distribute or transfer the
Program except as expressly provided under this General Public License.
Any attempt otherwise to copy, modify, sublicense, distribute or transfer
the Program is void, and will automatically terminate your rights to use
the Program under this License. However, parties who have received
copies, or rights to use copies, from you under this General Public
License will not have their licenses terminated so long as such parties
remain in full compliance.
<LI>
By copying, distributing or modifying the Program (or any work based
on the Program) you indicate your acceptance of this license to do so,
and all its terms and conditions.
<LI>
Each time you redistribute the Program (or any work based on the
Program), the recipient automatically receives a license from the original
licensor to copy, distribute or modify the Program subject to these
terms and conditions. You may not impose any further restrictions on the
recipients' exercise of the rights granted herein.
<LI>
The Free Software Foundation may publish revised and/or new versions
of the General Public License from time to time. Such new versions will
be similar in spirit to the present version, but may differ in detail to
address new problems or concerns.
Each version is given a distinguishing version number. If the Program
specifies a version number of the license which applies to it and "any
later version", you have the option of following the terms and conditions
either of that version or of any later version published by the Free
Software Foundation. If the Program does not specify a version number of
the license, you may choose any version ever published by the Free Software
Foundation.
<LI>
If you wish to incorporate parts of the Program into other free
programs whose distribution conditions are different, write to the author
to ask for permission. For software which is copyrighted by the Free
Software Foundation, write to the Free Software Foundation; we sometimes
make exceptions for this. Our decision will be guided by the two goals
of preserving the free status of all derivatives of our free software and
of promoting the sharing and reuse of software generally.
NO WARRANTY
<LI>
BECAUSE THE PROGRAM IS LICENSED FREE OF CHARGE, THERE IS NO WARRANTY
FOR THE PROGRAM, TO THE EXTENT PERMITTED BY APPLICABLE LAW. EXCEPT WHEN
OTHERWISE STATED IN WRITING THE COPYRIGHT HOLDERS AND/OR OTHER PARTIES
PROVIDE THE PROGRAM "AS IS" WITHOUT WARRANTY OF ANY KIND, EITHER EXPRESSED
OR IMPLIED, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES OF
MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE. THE ENTIRE RISK AS
TO THE QUALITY AND PERFORMANCE OF THE PROGRAM IS WITH YOU. SHOULD THE
PROGRAM PROVE DEFECTIVE, YOU ASSUME THE COST OF ALL NECESSARY SERVICING,
REPAIR OR CORRECTION.
<LI>
IN NO EVENT UNLESS REQUIRED BY APPLICABLE LAW OR AGREED TO IN WRITING WILL
ANY COPYRIGHT HOLDER, OR ANY OTHER PARTY WHO MAY MODIFY AND/OR
REDISTRIBUTE THE PROGRAM AS PERMITTED ABOVE, BE LIABLE TO YOU FOR DAMAGES,
INCLUDING ANY GENERAL, SPECIAL, INCIDENTAL OR CONSEQUENTIAL DAMAGES
ARISING OUT OF THE USE OR INABILITY TO USE THE PROGRAM (INCLUDING BUT NOT
LIMITED TO LOSS OF DATA OR DATA BEING RENDERED INACCURATE OR LOSSES
SUSTAINED BY YOU OR THIRD PARTIES OR A FAILURE OF THE PROGRAM TO OPERATE
WITH ANY OTHER PROGRAMS), EVEN IF SUCH HOLDER OR OTHER PARTY HAS BEEN
ADVISED OF THE POSSIBILITY OF SUCH DAMAGES.
</OL>
<P>
END OF TERMS AND CONDITIONS
</P>
<H2><A NAME="SEC4" HREF="gperf_toc.html#TOC4">Appendix: How to Apply These Terms to Your New Programs</A></H2>
<P>
If you develop a new program, and you want it to be of the greatest
possible use to humanity, the best way to achieve this is to make it
free software which everyone can redistribute and change under these
terms.
</P>
<P>
To do so, attach the following notices to the program. It is safest to
attach them to the start of each source file to most effectively convey
the exclusion of warranty; and each file should have at least the
"copyright" line and a pointer to where the full notice is found.
</P>
<PRE>
<VAR>one line to give the program's name and a brief idea of what it does.</VAR>
Copyright (C) 19<VAR>yy</VAR> <VAR>name of author</VAR>
This program is free software; you can redistribute it and/or modify
it under the terms of the GNU General Public License as published by
the Free Software Foundation; either version 1, or (at your option)
any later version.
This program is distributed in the hope that it will be useful,
but WITHOUT ANY WARRANTY; without even the implied warranty of
MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
GNU General Public License for more details.
You should have received a copy of the GNU General Public License
along with this program; if not, write to the Free Software
Foundation, Inc., 59 Temple Place - Suite 330, Boston, MA 02111-1307, USA.
</PRE>
<P>
Also add information on how to contact you by electronic and paper mail.
</P>
<P>
If the program is interactive, make it output a short notice like this
when it starts in an interactive mode:
</P>
<PRE>
Gnomovision version 69, Copyright (C) 19<VAR>yy</VAR> <VAR>name of author</VAR>
Gnomovision comes with ABSOLUTELY NO WARRANTY; for details type `show w'.
This is free software, and you are welcome to redistribute it
under certain conditions; type `show c' for details.
</PRE>
<P>
The hypothetical commands `show w' and `show c' should show the
appropriate parts of the General Public License. Of course, the
commands you use may be called something other than `show w' and `show
c'; they could even be mouse-clicks or menu items--whatever suits your
program.
</P>
<P>
You should also get your employer (if you work as a programmer) or your
school, if any, to sign a "copyright disclaimer" for the program, if
necessary. Here a sample; alter the names:
</P>
<PRE>
Yoyodyne, Inc., hereby disclaims all copyright interest in the
program `Gnomovision' (a program to direct compilers to make passes
at assemblers) written by James Hacker.
<VAR>signature of Ty Coon</VAR>, 1 April 1989
Ty Coon, President of Vice
</PRE>
<P>
That's all there is to it!
</P>
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</HEAD> </HEAD>
<BODY> <BODY>
Go to the <A HREF="gperf_1.html">first</A>, <A HREF="gperf_2.html">previous</A>, <A HREF="gperf_4.html">next</A>, <A HREF="gperf_11.html">last</A> section, <A HREF="gperf_toc.html">table of contents</A>. Go to the <A HREF="gperf_1.html">first</A>, <A HREF="gperf_2.html">previous</A>, <A HREF="gperf_4.html">next</A>, <A HREF="gperf_11.html">last</A> section, <A HREF="gperf_toc.html">table of contents</A>.
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<H1><A NAME="SEC5" HREF="gperf_toc.html#TOC5">Contributors to GNU <CODE>gperf</CODE> Utility</A></H1> <H1><A NAME="SEC5" HREF="gperf_toc.html#TOC5">1 Introduction</A></H1>
<P>
<CODE>gperf</CODE> is a perfect hash function generator written in C++. It
transforms an <VAR>n</VAR> element user-specified keyword set <VAR>W</VAR> into a
perfect hash function <VAR>F</VAR>. <VAR>F</VAR> uniquely maps keywords in
<VAR>W</VAR> onto the range 0..<VAR>k</VAR>, where <VAR>k</VAR> &#62;= <VAR>n</VAR>. If <VAR>k</VAR>
= <VAR>n</VAR> then <VAR>F</VAR> is a <EM>minimal</EM> perfect hash function.
<CODE>gperf</CODE> generates a 0..<VAR>k</VAR> element static lookup table and a
pair of C functions. These functions determine whether a given
character string <VAR>s</VAR> occurs in <VAR>W</VAR>, using at most one probe into
the lookup table.
<UL> </P>
<LI> <P>
<CODE>gperf</CODE> currently generates the reserved keyword recognizer for
The GNU <CODE>gperf</CODE> perfect hash function generator utility was lexical analyzers in several production and research compilers and
originally written in GNU C++ by Douglas C. Schmidt. It is now also language processing tools, including GNU C, GNU C++, GNU Pascal, GNU
available in a highly-portable "old-style" C version. The general Modula 3, and GNU indent. Complete C++ source code for <CODE>gperf</CODE> is
idea for the perfect hash function generator was inspired by Keith available via anonymous ftp from <CODE>ftp://ftp.gnu.org/pub/gnu/gperf/</CODE>.
Bostic's algorithm written in C, and distributed to net.sources around A paper describing <CODE>gperf</CODE>'s design and implementation in greater
1984. The current program is a heavily modified, enhanced, and extended detail is available in the Second USENIX C++ Conference proceedings.
implementation of Keith's basic idea, created at the University of
California, Irvine. Bugs, patches, and suggestions should be reported
to <CODE>&#60;bug-gnu-utils@gnu.org&#62;</CODE> and <CODE>&#60;schmidt@ics.uci.edu&#62;</CODE>.
<LI>
Special thanks is extended to Michael Tiemann and Doug Lea, for
providing a useful compiler, and for giving me a forum to exhibit my
creation.
In addition, Adam de Boor and Nels Olson provided many tips and insights
that greatly helped improve the quality and functionality of <CODE>gperf</CODE>.
</UL>
</P>
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</HEAD> </HEAD>
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<H1><A NAME="SEC6" HREF="gperf_toc.html#TOC6">1 Introduction</A></H1> <H1><A NAME="SEC6" HREF="gperf_toc.html#TOC6">2 Static search structures and GNU <CODE>gperf</CODE></A></H1>
<P> <P>
<CODE>gperf</CODE> is a perfect hash function generator written in C++. It <A NAME="IDX2"></A>
transforms an <VAR>n</VAR> element user-specified keyword set <VAR>W</VAR> into
a perfect hash function <VAR>F</VAR>. <VAR>F</VAR> uniquely maps keywords in
<VAR>W</VAR> onto the range 0..<VAR>k</VAR>, where <VAR>k &#62;= n</VAR>. If
<VAR>k = n</VAR> then <VAR>F</VAR> is a <EM>minimal</EM> perfect hash function.
<CODE>gperf</CODE> generates a 0..<VAR>k</VAR> element static lookup table and a
pair of C functions. These functions determine whether a given
character string <VAR>s</VAR> occurs in <VAR>W</VAR>, using at most one probe
into the lookup table.
</P> </P>
<P> <P>
<CODE>gperf</CODE> currently generates the reserved keyword recognizer for A <STRONG>static search structure</STRONG> is an Abstract Data Type with certain
lexical analyzers in several production and research compilers and fundamental operations, e.g., <EM>initialize</EM>, <EM>insert</EM>,
language processing tools, including GNU C, GNU C++, GNU Pascal, GNU and <EM>retrieve</EM>. Conceptually, all insertions occur before any
Modula 3, and GNU indent. Complete C++ source code for <CODE>gperf</CODE> is retrievals. In practice, <CODE>gperf</CODE> generates a <CODE>static</CODE> array
available via anonymous ftp from <CODE>ics.uci.edu</CODE> and containing search set keywords and any associated attributes specified
<CODE>ftp.santafe.edu</CODE>. <CODE>gperf</CODE> was also distributed along with by the user. Thus, there is essentially no execution-time cost for the
the GNU libg++ library for several years. A highly portable, insertions. It is a useful data structure for representing <EM>static
functionally equivalent K&#38;R C version of <CODE>gperf</CODE> is archived in search sets</EM>. Static search sets occur frequently in software system
comp.sources.unix, volume 20. Finally, a paper describing applications. Typical static search sets include compiler reserved
<CODE>gperf</CODE>'s design and implementation in greater detail is available words, assembler instruction opcodes, and built-in shell interpreter
in the Second USENIX C++ Conference proceedings. commands. Search set members, called <STRONG>keywords</STRONG>, are inserted into
the structure only once, usually during program initialization, and are
not generally modified at run-time.
</P>
<P>
Numerous static search structure implementations exist, e.g.,
arrays, linked lists, binary search trees, digital search tries, and
hash tables. Different approaches offer trade-offs between space
utilization and search time efficiency. For example, an <VAR>n</VAR> element
sorted array is space efficient, though the average-case time
complexity for retrieval operations using binary search is
proportional to log <VAR>n</VAR>. Conversely, hash table implementations
often locate a table entry in constant time, but typically impose
additional memory overhead and exhibit poor worst case performance.
</P>
<P>
<A NAME="IDX3"></A>
<EM>Minimal perfect hash functions</EM> provide an optimal solution for a
particular class of static search sets. A minimal perfect hash
function is defined by two properties:
</P>
<UL>
<LI>
It allows keyword recognition in a static search set using at most
<EM>one</EM> probe into the hash table. This represents the "perfect"
property.
<LI>
The actual memory allocated to store the keywords is precisely large
enough for the keyword set, and <EM>no larger</EM>. This is the
"minimal" property.
</UL>
<P>
For most applications it is far easier to generate <EM>perfect</EM> hash
functions than <EM>minimal perfect</EM> hash functions. Moreover,
non-minimal perfect hash functions frequently execute faster than
minimal ones in practice. This phenomena occurs since searching a
sparse keyword table increases the probability of locating a "null"
entry, thereby reducing string comparisons. <CODE>gperf</CODE>'s default
behavior generates <EM>near-minimal</EM> perfect hash functions for
keyword sets. However, <CODE>gperf</CODE> provides many options that permit
user control over the degree of minimality and perfection.
</P>
<P>
Static search sets often exhibit relative stability over time. For
example, Ada's 63 reserved words have remained constant for nearly a
decade. It is therefore frequently worthwhile to expend concerted
effort building an optimal search structure <EM>once</EM>, if it
subsequently receives heavy use multiple times. <CODE>gperf</CODE> removes
the drudgery associated with constructing time- and space-efficient
search structures by hand. It has proven a useful and practical tool
for serious programming projects. Output from <CODE>gperf</CODE> is currently
used in several production and research compilers, including GNU C, GNU
C++, GNU Pascal, and GNU Modula 3. The latter two compilers are not yet
part of the official GNU distribution. Each compiler utilizes
<CODE>gperf</CODE> to automatically generate static search structures that
efficiently identify their respective reserved keywords.
</P> </P>
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<H1><A NAME="SEC7" HREF="gperf_toc.html#TOC7">2 Static search structures and GNU <CODE>gperf</CODE></A></H1> <H1><A NAME="SEC7" HREF="gperf_toc.html#TOC7">3 High-Level Description of GNU <CODE>gperf</CODE></A></H1>
<P> <P>
A <STRONG>static search structure</STRONG> is an Abstract Data Type with certain The perfect hash function generator <CODE>gperf</CODE> reads a set of
fundamental operations, e.g., <EM>initialize</EM>, <EM>insert</EM>, "keywords" from a <STRONG>keyfile</STRONG> (or from the standard input by
and <EM>retrieve</EM>. Conceptually, all insertions occur before any default). It attempts to derive a perfect hashing function that
retrievals. In practice, <CODE>gperf</CODE> generates a <CODE>static</CODE> array recognizes a member of the <STRONG>static keyword set</STRONG> with at most a
containing search set keywords and any associated attributes specified single probe into the lookup table. If <CODE>gperf</CODE> succeeds in
by the user. Thus, there is essentially no execution-time cost for the generating such a function it produces a pair of C source code routines
insertions. It is a useful data structure for representing <EM>static that perform hashing and table lookup recognition. All generated C code
search sets</EM>. Static search sets occur frequently in software system is directed to the standard output. Command-line options described
applications. Typical static search sets include compiler reserved below allow you to modify the input and output format to <CODE>gperf</CODE>.
words, assembler instruction opcodes, and built-in shell interpreter
commands. Search set members, called <STRONG>keywords</STRONG>, are inserted into
the structure only once, usually during program initialization, and are
not generally modified at run-time.
</P> </P>
<P> <P>
Numerous static search structure implementations exist, e.g., By default, <CODE>gperf</CODE> attempts to produce time-efficient code, with
arrays, linked lists, binary search trees, digital search tries, and less emphasis on efficient space utilization. However, several options
hash tables. Different approaches offer trade-offs between space exist that permit trading-off execution time for storage space and vice
utilization and search time efficiency. For example, an <VAR>n</VAR> element versa. In particular, expanding the generated table size produces a
sorted array is space efficient, though the average-case time sparse search structure, generally yielding faster searches.
complexity for retrieval operations using binary search is Conversely, you can direct <CODE>gperf</CODE> to utilize a C <CODE>switch</CODE>
proportional to log <VAR>n</VAR>. Conversely, hash table implementations statement scheme that minimizes data space storage size. Furthermore,
often locate a table entry in constant time, but typically impose using a C <CODE>switch</CODE> may actually speed up the keyword retrieval time
additional memory overhead and exhibit poor worst case performance. somewhat. Actual results depend on your C compiler, of course.
</P>
<P>
<EM>Minimal perfect hash functions</EM> provide an optimal solution for a
particular class of static search sets. A minimal perfect hash
function is defined by two properties:
</P>
<UL>
<LI>
It allows keyword recognition in a static search set using at most
<EM>one</EM> probe into the hash table. This represents the "perfect"
property.
<LI>
The actual memory allocated to store the keywords is precisely large
enough for the keyword set, and <EM>no larger</EM>. This is the
"minimal" property.
</UL>
<P>
For most applications it is far easier to generate <EM>perfect</EM> hash
functions than <EM>minimal perfect</EM> hash functions. Moreover,
non-minimal perfect hash functions frequently execute faster than
minimal ones in practice. This phenomena occurs since searching a
sparse keyword table increases the probability of locating a "null"
entry, thereby reducing string comparisons. <CODE>gperf</CODE>'s default
behavior generates <EM>near-minimal</EM> perfect hash functions for
keyword sets. However, <CODE>gperf</CODE> provides many options that permit
user control over the degree of minimality and perfection.
</P> </P>
<P> <P>
Static search sets often exhibit relative stability over time. For In general, <CODE>gperf</CODE> assigns values to the characters it is using
example, Ada's 63 reserved words have remained constant for nearly a for hashing until some set of values gives each keyword a unique value.
decade. It is therefore frequently worthwhile to expend concerted A helpful heuristic is that the larger the hash value range, the easier
effort building an optimal search structure <EM>once</EM>, if it it is for <CODE>gperf</CODE> to find and generate a perfect hash function.
subsequently receives heavy use multiple times. <CODE>gperf</CODE> removes Experimentation is the key to getting the most from <CODE>gperf</CODE>.
the drudgery associated with constructing time- and space-efficient
search structures by hand. It has proven a useful and practical tool </P>
for serious programming projects. Output from <CODE>gperf</CODE> is currently
used in several production and research compilers, including GNU C, GNU
C++, GNU Pascal, and GNU Modula 3. The latter two compilers are not yet <H2><A NAME="SEC8" HREF="gperf_toc.html#TOC8">3.1 Input Format to <CODE>gperf</CODE></A></H2>
part of the official GNU distribution. Each compiler utilizes <P>
<CODE>gperf</CODE> to automatically generate static search structures that <A NAME="IDX4"></A>
efficiently identify their respective reserved keywords. <A NAME="IDX5"></A>
<A NAME="IDX6"></A>
<A NAME="IDX7"></A>
You can control the input keyfile format by varying certain command-line
arguments, in particular the <SAMP>`-t'</SAMP> option. The input's appearance
is similar to GNU utilities <CODE>flex</CODE> and <CODE>bison</CODE> (or UNIX
utilities <CODE>lex</CODE> and <CODE>yacc</CODE>). Here's an outline of the general
format:
</P>
<PRE>
declarations
%%
keywords
%%
functions
</PRE>
<P>
<EM>Unlike</EM> <CODE>flex</CODE> or <CODE>bison</CODE>, all sections of
<CODE>gperf</CODE>'s input are optional. The following sections describe the
input format for each section.
</P>
<H3><A NAME="SEC9" HREF="gperf_toc.html#TOC9">3.1.1 <CODE>struct</CODE> Declarations and C Code Inclusion</A></H3>
<P>
The keyword input file optionally contains a section for including
arbitrary C declarations and definitions, as well as provisions for
providing a user-supplied <CODE>struct</CODE>. If the <SAMP>`-t'</SAMP> option
<EM>is</EM> enabled, you <EM>must</EM> provide a C <CODE>struct</CODE> as the last
component in the declaration section from the keyfile file. The first
field in this struct must be a <CODE>char *</CODE> or <CODE>const char *</CODE>
identifier called <SAMP>`name'</SAMP>, although it is possible to modify this
field's name with the <SAMP>`-K'</SAMP> option described below.
</P>
<P>
Here is a simple example, using months of the year and their attributes as
input:
</P>
<PRE>
struct months { char *name; int number; int days; int leap_days; };
%%
january, 1, 31, 31
february, 2, 28, 29
march, 3, 31, 31
april, 4, 30, 30
may, 5, 31, 31
june, 6, 30, 30
july, 7, 31, 31
august, 8, 31, 31
september, 9, 30, 30
october, 10, 31, 31
november, 11, 30, 30
december, 12, 31, 31
</PRE>
<P>
<A NAME="IDX8"></A>
Separating the <CODE>struct</CODE> declaration from the list of keywords and
other fields are a pair of consecutive percent signs, <SAMP>`%%'</SAMP>,
appearing left justified in the first column, as in the UNIX utility
<CODE>lex</CODE>.
</P>
<P>
<A NAME="IDX9"></A>
<A NAME="IDX10"></A>
Using a syntax similar to GNU utilities <CODE>flex</CODE> and <CODE>bison</CODE>, it
is possible to directly include C source text and comments verbatim into
the generated output file. This is accomplished by enclosing the region
inside left-justified surrounding <SAMP>`%{'</SAMP>, <SAMP>`%}'</SAMP> pairs. Here is
an input fragment based on the previous example that illustrates this
feature:
</P>
<PRE>
%{
#include &#60;assert.h&#62;
/* This section of code is inserted directly into the output. */
int return_month_days (struct months *months, int is_leap_year);
%}
struct months { char *name; int number; int days; int leap_days; };
%%
january, 1, 31, 31
february, 2, 28, 29
march, 3, 31, 31
...
</PRE>
<P>
It is possible to omit the declaration section entirely. In this case
the keyfile begins directly with the first keyword line, e.g.:
</P>
<PRE>
january, 1, 31, 31
february, 2, 28, 29
march, 3, 31, 31
april, 4, 30, 30
...
</PRE>
<H3><A NAME="SEC10" HREF="gperf_toc.html#TOC10">3.1.2 Format for Keyword Entries</A></H3>
<P>
The second keyfile format section contains lines of keywords and any
associated attributes you might supply. A line beginning with <SAMP>`#'</SAMP>
in the first column is considered a comment. Everything following the
<SAMP>`#'</SAMP> is ignored, up to and including the following newline.
</P>
<P>
The first field of each non-comment line is always the key itself. It
can be given in two ways: as a simple name, i.e., without surrounding
string quotation marks, or as a string enclosed in double-quotes, in
C syntax, possibly with backslash escapes like <CODE>\"</CODE> or <CODE>\234</CODE>
or <CODE>\xa8</CODE>. In either case, it must start right at the beginning
of the line, without leading whitespace.
In this context, a "field" is considered to extend up to, but
not include, the first blank, comma, or newline. Here is a simple
example taken from a partial list of C reserved words:
</P>
<PRE>
# These are a few C reserved words, see the c.gperf file
# for a complete list of ANSI C reserved words.
unsigned
sizeof
switch
signed
if
default
for
while
return
</PRE>
<P>
Note that unlike <CODE>flex</CODE> or <CODE>bison</CODE> the first <SAMP>`%%'</SAMP> marker
may be elided if the declaration section is empty.
</P>
<P>
Additional fields may optionally follow the leading keyword. Fields
should be separated by commas, and terminate at the end of line. What
these fields mean is entirely up to you; they are used to initialize the
elements of the user-defined <CODE>struct</CODE> provided by you in the
declaration section. If the <SAMP>`-t'</SAMP> option is <EM>not</EM> enabled
these fields are simply ignored. All previous examples except the last
one contain keyword attributes.
</P>
<H3><A NAME="SEC11" HREF="gperf_toc.html#TOC11">3.1.3 Including Additional C Functions</A></H3>
<P>
The optional third section also corresponds closely with conventions
found in <CODE>flex</CODE> and <CODE>bison</CODE>. All text in this section,
starting at the final <SAMP>`%%'</SAMP> and extending to the end of the input
file, is included verbatim into the generated output file. Naturally,
it is your responsibility to ensure that the code contained in this
section is valid C.
</P>
<H2><A NAME="SEC12" HREF="gperf_toc.html#TOC12">3.2 Output Format for Generated C Code with <CODE>gperf</CODE></A></H2>
<P>
<A NAME="IDX11"></A>
</P>
<P>
Several options control how the generated C code appears on the standard
output. Two C function are generated. They are called <CODE>hash</CODE> and
<CODE>in_word_set</CODE>, although you may modify their names with a command-line
option. Both functions require two arguments, a string, <CODE>char *</CODE>
<VAR>str</VAR>, and a length parameter, <CODE>int</CODE> <VAR>len</VAR>. Their default
function prototypes are as follows:
</P>
<P>
<DL>
<DT><U>Function:</U> unsigned int <B>hash</B> <I>(const char * <VAR>str</VAR>, unsigned int <VAR>len</VAR>)</I>
<DD><A NAME="IDX12"></A>
By default, the generated <CODE>hash</CODE> function returns an integer value
created by adding <VAR>len</VAR> to several user-specified <VAR>str</VAR> key
positions indexed into an <STRONG>associated values</STRONG> table stored in a
local static array. The associated values table is constructed
internally by <CODE>gperf</CODE> and later output as a static local C array
called <SAMP>`hash_table'</SAMP>; its meaning and properties are described below
(see section <A HREF="gperf_9.html#SEC22">7 Implementation Details of GNU <CODE>gperf</CODE></A>). The relevant key positions are specified via
the <SAMP>`-k'</SAMP> option when running <CODE>gperf</CODE>, as detailed in the
<EM>Options</EM> section below(see section <A HREF="gperf_6.html#SEC14">4 Invoking <CODE>gperf</CODE></A>).
</DL>
</P>
<P>
<DL>
<DT><U>Function:</U> <B>in_word_set</B> <I>(const char * <VAR>str</VAR>, unsigned int <VAR>len</VAR>)</I>
<DD><A NAME="IDX13"></A>
If <VAR>str</VAR> is in the keyword set, returns a pointer to that
keyword. More exactly, if the option <SAMP>`-t'</SAMP> was given, it returns
a pointer to the matching keyword's structure. Otherwise it returns
<CODE>NULL</CODE>.
</DL>
</P>
<P>
If the option <SAMP>`-c'</SAMP> is not used, <VAR>str</VAR> must be a NUL terminated
string of exactly length <VAR>len</VAR>. If <SAMP>`-c'</SAMP> is used, <VAR>str</VAR> must
simply be an array of <VAR>len</VAR> characters and does not need to be NUL
terminated.
</P>
<P>
The code generated for these two functions is affected by the following
options:
</P>
<DL COMPACT>
<DT><SAMP>`-t'</SAMP>
<DD>
<DT><SAMP>`--struct-type'</SAMP>
<DD>
Make use of the user-defined <CODE>struct</CODE>.
<DT><SAMP>`-S <VAR>total-switch-statements</VAR>'</SAMP>
<DD>
<DT><SAMP>`--switch=<VAR>total-switch-statements</VAR>'</SAMP>
<DD>
<A NAME="IDX14"></A>
Generate 1 or more C <CODE>switch</CODE> statement rather than use a large,
(and potentially sparse) static array. Although the exact time and
space savings of this approach vary according to your C compiler's
degree of optimization, this method often results in smaller and faster
code.
</DL>
<P>
If the <SAMP>`-t'</SAMP> and <SAMP>`-S'</SAMP> options are omitted, the default action
is to generate a <CODE>char *</CODE> array containing the keys, together with
additional null strings used for padding the array. By experimenting
with the various input and output options, and timing the resulting C
code, you can determine the best option choices for different keyword
set characteristics.
</P>
<H2><A NAME="SEC13" HREF="gperf_toc.html#TOC13">3.3 Use of NUL characters</A></H2>
<P>
<A NAME="IDX15"></A>
</P>
<P>
By default, the code generated by <CODE>gperf</CODE> operates on zero
terminated strings, the usual representation of strings in C. This means
that the keywords in the input file must not contain NUL characters,
and the <VAR>str</VAR> argument passed to <CODE>hash</CODE> or <CODE>in_word_set</CODE>
must be NUL terminated and have exactly length <VAR>len</VAR>.
</P>
<P>
If option <SAMP>`-c'</SAMP> is used, then the <VAR>str</VAR> argument does not need
to be NUL terminated. The code generated by <CODE>gperf</CODE> will only
access the first <VAR>len</VAR>, not <VAR>len+1</VAR>, bytes starting at <VAR>str</VAR>.
However, the keywords in the input file still must not contain NUL
characters.
</P>
<P>
If option <SAMP>`-l'</SAMP> is used, then the hash table performs binary
comparison. The keywords in the input file may contain NUL characters,
written in string syntax as <CODE>\000</CODE> or <CODE>\x00</CODE>, and the code
generated by <CODE>gperf</CODE> will treat NUL like any other character.
Also, in this case the <SAMP>`-c'</SAMP> option is ignored.
</P> </P>
<P><HR><P> <P><HR><P>

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</HEAD> </HEAD>
<BODY> <BODY>
Go to the <A HREF="gperf_1.html">first</A>, <A HREF="gperf_5.html">previous</A>, <A HREF="gperf_7.html">next</A>, <A HREF="gperf_11.html">last</A> section, <A HREF="gperf_toc.html">table of contents</A>. Go to the <A HREF="gperf_1.html">first</A>, <A HREF="gperf_5.html">previous</A>, <A HREF="gperf_7.html">next</A>, <A HREF="gperf_11.html">last</A> section, <A HREF="gperf_toc.html">table of contents</A>.
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<H1><A NAME="SEC8" HREF="gperf_toc.html#TOC8">3 High-Level Description of GNU <CODE>gperf</CODE></A></H1> <H1><A NAME="SEC14" HREF="gperf_toc.html#TOC14">4 Invoking <CODE>gperf</CODE></A></H1>
<P> <P>
The perfect hash function generator <CODE>gperf</CODE> reads a set of There are <EM>many</EM> options to <CODE>gperf</CODE>. They were added to make
"keywords" from a <STRONG>keyfile</STRONG> (or from the standard input by the program more convenient for use with real applications. "On-line"
default). It attempts to derive a perfect hashing function that help is readily available via the <SAMP>`-h'</SAMP> option. Here is the
recognizes a member of the <STRONG>static keyword set</STRONG> with at most a complete list of options.
single probe into the lookup table. If <CODE>gperf</CODE> succeeds in
generating such a function it produces a pair of C source code routines
that perform hashing and table lookup recognition. All generated C code
is directed to the standard output. Command-line options described
below allow you to modify the input and output format to <CODE>gperf</CODE>.
</P>
<P>
By default, <CODE>gperf</CODE> attempts to produce time-efficient code, with
less emphasis on efficient space utilization. However, several options
exist that permit trading-off execution time for storage space and vice
versa. In particular, expanding the generated table size produces a
sparse search structure, generally yielding faster searches.
Conversely, you can direct <CODE>gperf</CODE> to utilize a C <CODE>switch</CODE>
statement scheme that minimizes data space storage size. Furthermore,
using a C <CODE>switch</CODE> may actually speed up the keyword retrieval time
somewhat. Actual results depend on your C compiler, of course.
</P>
<P>
In general, <CODE>gperf</CODE> assigns values to the characters it is using
for hashing until some set of values gives each keyword a unique value.
A helpful heuristic is that the larger the hash value range, the easier
it is for <CODE>gperf</CODE> to find and generate a perfect hash function.
Experimentation is the key to getting the most from <CODE>gperf</CODE>.
</P>
<H2><A NAME="SEC9" HREF="gperf_toc.html#TOC9">3.1 Input Format to <CODE>gperf</CODE></A></H2>
<P>
You can control the input keyfile format by varying certain command-line
arguments, in particular the <SAMP>`-t'</SAMP> option. The input's appearance
is similar to GNU utilities <CODE>flex</CODE> and <CODE>bison</CODE> (or UNIX
utilities <CODE>lex</CODE> and <CODE>yacc</CODE>). Here's an outline of the general
format:
</P>
<PRE>
declarations
%%
keywords
%%
functions
</PRE>
<P>
<EM>Unlike</EM> <CODE>flex</CODE> or <CODE>bison</CODE>, all sections of <CODE>gperf</CODE>'s input
are optional. The following sections describe the input format for each
section.
</P> </P>
<H3><A NAME="SEC10" HREF="gperf_toc.html#TOC10">3.1.1 <CODE>struct</CODE> Declarations and C Code Inclusion</A></H3> <H2><A NAME="SEC15" HREF="gperf_toc.html#TOC15">4.1 Options that affect Interpretation of the Input File</A></H2>
<P>
The keyword input file optionally contains a section for including
arbitrary C declarations and definitions, as well as provisions for
providing a user-supplied <CODE>struct</CODE>. If the <SAMP>`-t'</SAMP> option
<EM>is</EM> enabled, you <EM>must</EM> provide a C <CODE>struct</CODE> as the last
component in the declaration section from the keyfile file. The first
field in this struct must be a <CODE>char *</CODE> identifier called <SAMP>`name'</SAMP>,
although it is possible to modify this field's name with the <SAMP>`-K'</SAMP>
option described below.
</P>
<P>
Here is simple example, using months of the year and their attributes as
input:
</P>
<PRE>
struct months { char *name; int number; int days; int leap_days; };
%%
january, 1, 31, 31
february, 2, 28, 29
march, 3, 31, 31
april, 4, 30, 30
may, 5, 31, 31
june, 6, 30, 30
july, 7, 31, 31
august, 8, 31, 31
september, 9, 30, 30
october, 10, 31, 31
november, 11, 30, 30
december, 12, 31, 31
</PRE>
<P>
Separating the <CODE>struct</CODE> declaration from the list of key words and
other fields are a pair of consecutive percent signs, <CODE>%%</CODE>,
appearing left justified in the first column, as in the UNIX utility
<CODE>lex</CODE>.
</P>
<P>
Using a syntax similar to GNU utilities <CODE>flex</CODE> and <CODE>bison</CODE>, it
is possible to directly include C source text and comments verbatim into
the generated output file. This is accomplished by enclosing the region
inside left-justified surrounding <CODE>%{</CODE>, <CODE>%}</CODE> pairs. Here is
an input fragment based on the previous example that illustrates this
feature:
</P>
<PRE>
%{
#include &#60;assert.h&#62;
/* This section of code is inserted directly into the output. */
int return_month_days (struct months *months, int is_leap_year);
%}
struct months { char *name; int number; int days; int leap_days; };
%%
january, 1, 31, 31
february, 2, 28, 29
march, 3, 31, 31
...
</PRE>
<P>
It is possible to omit the declaration section entirely. In this case
the keyfile begins directly with the first keyword line, e.g.:
</P>
<PRE>
january, 1, 31, 31
february, 2, 28, 29
march, 3, 31, 31
april, 4, 30, 30
...
</PRE>
<H3><A NAME="SEC11" HREF="gperf_toc.html#TOC11">3.1.2 Format for Keyword Entries</A></H3>
<P>
The second keyfile format section contains lines of keywords and any
associated attributes you might supply. A line beginning with <SAMP>`#'</SAMP>
in the first column is considered a comment. Everything following the
<SAMP>`#'</SAMP> is ignored, up to and including the following newline.
</P>
<P>
The first field of each non-comment line is always the key itself. It
should be given as a simple name, i.e., without surrounding
string quotation marks, and be left-justified flush against the first
column. In this context, a "field" is considered to extend up to, but
not include, the first blank, comma, or newline. Here is a simple
example taken from a partial list of C reserved words:
</P>
<PRE>
# These are a few C reserved words, see the c.<CODE>gperf</CODE> file
# for a complete list of ANSI C reserved words.
unsigned
sizeof
switch
signed
if
default
for
while
return
</PRE>
<P>
Note that unlike <CODE>flex</CODE> or <CODE>bison</CODE> the first <CODE>%%</CODE> marker
may be elided if the declaration section is empty.
</P>
<P>
Additional fields may optionally follow the leading keyword. Fields
should be separated by commas, and terminate at the end of line. What
these fields mean is entirely up to you; they are used to initialize the
elements of the user-defined <CODE>struct</CODE> provided by you in the
declaration section. If the <SAMP>`-t'</SAMP> option is <EM>not</EM> enabled
these fields are simply ignored. All previous examples except the last
one contain keyword attributes.
</P>
<H3><A NAME="SEC12" HREF="gperf_toc.html#TOC12">3.1.3 Including Additional C Functions</A></H3>
<P>
The optional third section also corresponds closely with conventions
found in <CODE>flex</CODE> and <CODE>bison</CODE>. All text in this section,
starting at the final <CODE>%%</CODE> and extending to the end of the input
file, is included verbatim into the generated output file. Naturally,
it is your responsibility to ensure that the code contained in this
section is valid C.
</P>
<H2><A NAME="SEC13" HREF="gperf_toc.html#TOC13">3.2 Output Format for Generated C Code with <CODE>gperf</CODE></A></H2>
<P>
Several options control how the generated C code appears on the standard
output. Two C function are generated. They are called <CODE>hash</CODE> and
<CODE>in_word_set</CODE>, although you may modify the name for
<CODE>in_word_set</CODE> with a command-line option. Both functions require
two arguments, a string, <CODE>char *</CODE> <VAR>str</VAR>, and a length
parameter, <CODE>int</CODE> <VAR>len</VAR>. Their default function prototypes are
as follows:
</P>
<PRE>
static int hash (char *str, int len);
int in_word_set (char *str, int len);
</PRE>
<P>
By default, the generated <CODE>hash</CODE> function returns an integer value
created by adding <VAR>len</VAR> to several user-specified <VAR>str</VAR> key
positions indexed into an <STRONG>associated values</STRONG> table stored in a
local static array. The associated values table is constructed
internally by <CODE>gperf</CODE> and later output as a static local C array called
<VAR>hash_table</VAR>; its meaning and properties are described below.
See section <A HREF="gperf_10.html#SEC22">7 Implementation Details of GNU <CODE>gperf</CODE></A>. The relevant key positions are specified via the
<SAMP>`-k'</SAMP> option when running <CODE>gperf</CODE>, as detailed in the <EM>Options</EM>
section below. See section <A HREF="gperf_7.html#SEC14">4 Options to the <CODE>gperf</CODE> Utility</A>.
</P>
<P>
Two options, <SAMP>`-g'</SAMP> (assume you are compiling with GNU C and its
<CODE>inline</CODE> feature) and <SAMP>`-a'</SAMP> (assume ANSI C-style function
prototypes), alter the content of both the generated <CODE>hash</CODE> and
<CODE>in_word_set</CODE> routines. However, function <CODE>in_word_set</CODE> may
be modified more extensively, in response to your option settings. The
options that affect the <CODE>in_word_set</CODE> structure are:
</P>
<UL>
<DL COMPACT> <DL COMPACT>
<DT><SAMP>`-e <VAR>keyword-delimiter-list</VAR>'</SAMP>
<DD>
<DT><SAMP>`--delimiters=<VAR>keyword-delimiter-list</VAR>'</SAMP>
<DD>
<A NAME="IDX16"></A>
Allows the user to provide a string containing delimiters used to
separate keywords from their attributes. The default is ",\n". This
option is essential if you want to use keywords that have embedded
commas or newlines. One useful trick is to use -e'TAB', where TAB is
the literal tab character.
<DT><SAMP>`-t'</SAMP> <DT><SAMP>`-t'</SAMP>
<DD> <DD>
Make use of the user-defined <CODE>struct</CODE>. <DT><SAMP>`--struct-type'</SAMP>
<DT><SAMP>`-S <VAR>total switch statements</VAR>'</SAMP>
<DD> <DD>
Generate 1 or more C <CODE>switch</CODE> statement rather than use a large, Allows you to include a <CODE>struct</CODE> type declaration for generated
(and potentially sparse) static array. Although the exact time and code. Any text before a pair of consecutive <SAMP>`%%'</SAMP> is considered
space savings of this approach vary according to your C compiler's part of the type declaration. Keywords and additional fields may follow
degree of optimization, this method often results in smaller and faster this, one group of fields per line. A set of examples for generating
code. perfect hash tables and functions for Ada, C, C++, Pascal, Modula 2,
Modula 3 and JavaScript reserved words are distributed with this release.
</DL> </DL>
<H2><A NAME="SEC16" HREF="gperf_toc.html#TOC16">4.2 Options to specify the Language for the Output Code</A></H2>
<DL COMPACT>
<DT><SAMP>`-L <VAR>generated-language-name</VAR>'</SAMP>
<DD>
<DT><SAMP>`--language=<VAR>generated-language-name</VAR>'</SAMP>
<DD>
Instructs <CODE>gperf</CODE> to generate code in the language specified by the
option's argument. Languages handled are currently:
<DL COMPACT>
<DT><SAMP>`KR-C'</SAMP>
<DD>
Old-style K&#38;R C. This language is understood by old-style C compilers and
ANSI C compilers, but ANSI C compilers may flag warnings (or even errors)
because of lacking <SAMP>`const'</SAMP>.
<DT><SAMP>`C'</SAMP>
<DD>
Common C. This language is understood by ANSI C compilers, and also by
old-style C compilers, provided that you <CODE>#define const</CODE> to empty
for compilers which don't know about this keyword.
<DT><SAMP>`ANSI-C'</SAMP>
<DD>
ANSI C. This language is understood by ANSI C compilers and C++ compilers.
<DT><SAMP>`C++'</SAMP>
<DD>
C++. This language is understood by C++ compilers.
</DL>
The default is C.
<DT><SAMP>`-a'</SAMP>
<DD>
This option is supported for compatibility with previous releases of
<CODE>gperf</CODE>. It does not do anything.
<DT><SAMP>`-g'</SAMP>
<DD>
This option is supported for compatibility with previous releases of
<CODE>gperf</CODE>. It does not do anything.
</DL>
<H2><A NAME="SEC17" HREF="gperf_toc.html#TOC17">4.3 Options for fine tuning Details in the Output Code</A></H2>
<DL COMPACT>
<DT><SAMP>`-K <VAR>key-name</VAR>'</SAMP>
<DD>
<DT><SAMP>`--slot-name=<VAR>key-name</VAR>'</SAMP>
<DD>
<A NAME="IDX17"></A>
This option is only useful when option <SAMP>`-t'</SAMP> has been given.
By default, the program assumes the structure component identifier for
the keyword is <SAMP>`name'</SAMP>. This option allows an arbitrary choice of
identifier for this component, although it still must occur as the first
field in your supplied <CODE>struct</CODE>.
<DT><SAMP>`-F <VAR>initializers</VAR>'</SAMP>
<DD>
<DT><SAMP>`--initializer-suffix=<VAR>initializers</VAR>'</SAMP>
<DD>
<A NAME="IDX18"></A>
This option is only useful when option <SAMP>`-t'</SAMP> has been given.
It permits to specify initializers for the structure members following
<VAR>key name</VAR> in empty hash table entries. The list of initializers
should start with a comma. By default, the emitted code will
zero-initialize structure members following <VAR>key name</VAR>.
<DT><SAMP>`-H <VAR>hash-function-name</VAR>'</SAMP>
<DD>
<DT><SAMP>`--hash-fn-name=<VAR>hash-function-name</VAR>'</SAMP>
<DD>
Allows you to specify the name for the generated hash function. Default
name is <SAMP>`hash'</SAMP>. This option permits the use of two hash tables in
the same file.
<DT><SAMP>`-N <VAR>lookup-function-name</VAR>'</SAMP>
<DD>
<DT><SAMP>`--lookup-fn-name=<VAR>lookup-function-name</VAR>'</SAMP>
<DD>
Allows you to specify the name for the generated lookup function.
Default name is <SAMP>`in_word_set'</SAMP>. This option permits completely
automatic generation of perfect hash functions, especially when multiple
generated hash functions are used in the same application.
<DT><SAMP>`-Z <VAR>class-name</VAR>'</SAMP>
<DD>
<DT><SAMP>`--class-name=<VAR>class-name</VAR>'</SAMP>
<DD>
<A NAME="IDX19"></A>
This option is only useful when option <SAMP>`-L C++'</SAMP> has been given. It
allows you to specify the name of generated C++ class. Default name is
<CODE>Perfect_Hash</CODE>.
<DT><SAMP>`-7'</SAMP>
<DD>
<DT><SAMP>`--seven-bit'</SAMP>
<DD>
This option specifies that all strings that will be passed as arguments
to the generated hash function and the generated lookup function will
solely consist of 7-bit ASCII characters (characters in the range 0..127).
(Note that the ANSI C functions <CODE>isalnum</CODE> and <CODE>isgraph</CODE> do
<EM>not</EM> guarantee that a character is in this range. Only an explicit
test like <SAMP>`c &#62;= 'A' &#38;&#38; c &#60;= 'Z''</SAMP> guarantees this.) This was the
default in versions of <CODE>gperf</CODE> earlier than 2.7; now the default is
to assume 8-bit characters.
<DT><SAMP>`-c'</SAMP>
<DD>
<DT><SAMP>`--compare-strncmp'</SAMP>
<DD>
Generates C code that uses the <CODE>strncmp</CODE> function to perform
string comparisons. The default action is to use <CODE>strcmp</CODE>.
<DT><SAMP>`-C'</SAMP>
<DD>
<DT><SAMP>`--readonly-tables'</SAMP>
<DD>
Makes the contents of all generated lookup tables constant, i.e.,
"readonly". Many compilers can generate more efficient code for this
by putting the tables in readonly memory.
<DT><SAMP>`-E'</SAMP>
<DD>
<DT><SAMP>`--enum'</SAMP>
<DD>
Define constant values using an enum local to the lookup function rather
than with #defines. This also means that different lookup functions can
reside in the same file. Thanks to James Clark <CODE>&#60;jjc@ai.mit.edu&#62;</CODE>.
<DT><SAMP>`-I'</SAMP>
<DD>
<DT><SAMP>`--includes'</SAMP>
<DD>
Include the necessary system include file, <CODE>&#60;string.h&#62;</CODE>, at the
beginning of the code. By default, this is not done; the user must
include this header file himself to allow compilation of the code.
<DT><SAMP>`-G'</SAMP>
<DD>
<DT><SAMP>`--global'</SAMP>
<DD>
Generate the static table of keywords as a static global variable,
rather than hiding it inside of the lookup function (which is the
default behavior).
<DT><SAMP>`-W <VAR>hash-table-array-name</VAR>'</SAMP>
<DD>
<DT><SAMP>`--word-array-name=<VAR>hash-table-array-name</VAR>'</SAMP>
<DD>
<A NAME="IDX20"></A>
Allows you to specify the name for the generated array containing the
hash table. Default name is <SAMP>`wordlist'</SAMP>. This option permits the
use of two hash tables in the same file, even when the option <SAMP>`-G'</SAMP>
is given.
<DT><SAMP>`-S <VAR>total-switch-statements</VAR>'</SAMP>
<DD>
<DT><SAMP>`--switch=<VAR>total-switch-statements</VAR>'</SAMP>
<DD>
<A NAME="IDX21"></A>
Causes the generated C code to use a <CODE>switch</CODE> statement scheme,
rather than an array lookup table. This can lead to a reduction in both
time and space requirements for some keyfiles. The argument to this
option determines how many <CODE>switch</CODE> statements are generated. A
value of 1 generates 1 <CODE>switch</CODE> containing all the elements, a
value of 2 generates 2 tables with 1/2 the elements in each
<CODE>switch</CODE>, etc. This is useful since many C compilers cannot
correctly generate code for large <CODE>switch</CODE> statements. This option
was inspired in part by Keith Bostic's original C program.
<DT><SAMP>`-T'</SAMP>
<DD>
<DT><SAMP>`--omit-struct-type'</SAMP>
<DD>
Prevents the transfer of the type declaration to the output file. Use
this option if the type is already defined elsewhere.
<DT><SAMP>`-p'</SAMP>
<DD>
This option is supported for compatibility with previous releases of
<CODE>gperf</CODE>. It does not do anything.
</DL>
<H2><A NAME="SEC18" HREF="gperf_toc.html#TOC18">4.4 Options for changing the Algorithms employed by <CODE>gperf</CODE></A></H2>
<DL COMPACT>
<DT><SAMP>`-k <VAR>keys</VAR>'</SAMP>
<DD>
<DT><SAMP>`--key-positions=<VAR>keys</VAR>'</SAMP>
<DD>
Allows selection of the character key positions used in the keywords'
hash function. The allowable choices range between 1-126, inclusive.
The positions are separated by commas, e.g., <SAMP>`-k 9,4,13,14'</SAMP>;
ranges may be used, e.g., <SAMP>`-k 2-7'</SAMP>; and positions may occur
in any order. Furthermore, the meta-character '*' causes the generated
hash function to consider <STRONG>all</STRONG> character positions in each key,
whereas '$' instructs the hash function to use the "final character"
of a key (this is the only way to use a character position greater than
126, incidentally).
For instance, the option <SAMP>`-k 1,2,4,6-10,'$''</SAMP> generates a hash
function that considers positions 1,2,4,6,7,8,9,10, plus the last
character in each key (which may differ for each key, obviously). Keys
with length less than the indicated key positions work properly, since
selected key positions exceeding the key length are simply not
referenced in the hash function.
<DT><SAMP>`-l'</SAMP>
<DD>
<DT><SAMP>`--compare-strlen'</SAMP>
<DD>
Compare key lengths before trying a string comparison. This might cut
down on the number of string comparisons made during the lookup, since
keys with different lengths are never compared via <CODE>strcmp</CODE>.
However, using <SAMP>`-l'</SAMP> might greatly increase the size of the
generated C code if the lookup table range is large (which implies that
the switch option <SAMP>`-S'</SAMP> is not enabled), since the length table
contains as many elements as there are entries in the lookup table.
This option is mandatory for binary comparisons (see section <A HREF="gperf_5.html#SEC13">3.3 Use of NUL characters</A>).
<DT><SAMP>`-D'</SAMP>
<DD>
<DT><SAMP>`--duplicates'</SAMP>
<DD>
<A NAME="IDX22"></A>
Handle keywords whose key position sets hash to duplicate values.
Duplicate hash values occur for two reasons:
<UL>
<LI>
Since <CODE>gperf</CODE> does not backtrack it is possible for it to process
all your input keywords without finding a unique mapping for each word.
However, frequently only a very small number of duplicates occur, and
the majority of keys still require one probe into the table.
<LI>
Sometimes a set of keys may have the same names, but possess different
attributes. With the -D option <CODE>gperf</CODE> treats all these keys as
part of an equivalence class and generates a perfect hash function with
multiple comparisons for duplicate keys. It is up to you to completely
disambiguate the keywords by modifying the generated C code. However,
<CODE>gperf</CODE> helps you out by organizing the output.
</UL> </UL>
<P> Option <SAMP>`-D'</SAMP> is extremely useful for certain large or highly
If the <SAMP>`-t'</SAMP> and <SAMP>`-S'</SAMP> options are omitted, the redundant keyword sets, e.g., assembler instruction opcodes.
default action is to generate a <CODE>char *</CODE> array containing the keys, Using this option usually means that the generated hash function is no
together with additional null strings used for padding the array. By longer perfect. On the other hand, it permits <CODE>gperf</CODE> to work on
experimenting with the various input and output options, and timing the keyword sets that it otherwise could not handle.
resulting C code, you can determine the best option choices for
different keyword set characteristics. <DT><SAMP>`-f <VAR>iteration-amount</VAR>'</SAMP>
<DD>
<DT><SAMP>`--fast=<VAR>iteration-amount</VAR>'</SAMP>
<DD>
Generate the perfect hash function "fast". This decreases
<CODE>gperf</CODE>'s running time at the cost of minimizing generated
table-size. The iteration amount represents the number of times to
iterate when resolving a collision. `0' means iterate by the number of
keywords. This option is probably most useful when used in conjunction
with options <SAMP>`-D'</SAMP> and/or <SAMP>`-S'</SAMP> for <EM>large</EM> keyword sets.
<DT><SAMP>`-i <VAR>initial-value</VAR>'</SAMP>
<DD>
<DT><SAMP>`--initial-asso=<VAR>initial-value</VAR>'</SAMP>
<DD>
Provides an initial <VAR>value</VAR> for the associate values array. Default
is 0. Increasing the initial value helps inflate the final table size,
possibly leading to more time efficient keyword lookups. Note that this
option is not particularly useful when <SAMP>`-S'</SAMP> is used. Also,
<SAMP>`-i'</SAMP> is overridden when the <SAMP>`-r'</SAMP> option is used.
<DT><SAMP>`-j <VAR>jump-value</VAR>'</SAMP>
<DD>
<DT><SAMP>`--jump=<VAR>jump-value</VAR>'</SAMP>
<DD>
<A NAME="IDX23"></A>
Affects the "jump value", i.e., how far to advance the associated
character value upon collisions. <VAR>Jump-value</VAR> is rounded up to an
odd number, the default is 5. If the <VAR>jump-value</VAR> is 0 <CODE>gperf</CODE>
jumps by random amounts.
<DT><SAMP>`-n'</SAMP>
<DD>
<DT><SAMP>`--no-strlen'</SAMP>
<DD>
Instructs the generator not to include the length of a keyword when
computing its hash value. This may save a few assembly instructions in
the generated lookup table.
<DT><SAMP>`-o'</SAMP>
<DD>
<DT><SAMP>`--occurrence-sort'</SAMP>
<DD>
Reorders the keywords by sorting the keywords so that frequently
occuring key position set components appear first. A second reordering
pass follows so that keys with "already determined values" are placed
towards the front of the keylist. This may decrease the time required
to generate a perfect hash function for many keyword sets, and also
produce more minimal perfect hash functions. The reason for this is
that the reordering helps prune the search time by handling inevitable
collisions early in the search process. On the other hand, if the
number of keywords is <EM>very</EM> large using <SAMP>`-o'</SAMP> may
<EM>increase</EM> <CODE>gperf</CODE>'s execution time, since collisions will
begin earlier and continue throughout the remainder of keyword
processing. See Cichelli's paper from the January 1980 Communications
of the ACM for details.
<DT><SAMP>`-r'</SAMP>
<DD>
<DT><SAMP>`--random'</SAMP>
<DD>
Utilizes randomness to initialize the associated values table. This
frequently generates solutions faster than using deterministic
initialization (which starts all associated values at 0). Furthermore,
using the randomization option generally increases the size of the
table. If <CODE>gperf</CODE> has difficultly with a certain keyword set try using
<SAMP>`-r'</SAMP> or <SAMP>`-D'</SAMP>.
<DT><SAMP>`-s <VAR>size-multiple</VAR>'</SAMP>
<DD>
<DT><SAMP>`--size-multiple=<VAR>size-multiple</VAR>'</SAMP>
<DD>
Affects the size of the generated hash table. The numeric argument for
this option indicates "how many times larger or smaller" the maximum
associated value range should be, in relationship to the number of keys.
If the <VAR>size-multiple</VAR> is negative the maximum associated value is
calculated by <EM>dividing</EM> it into the total number of keys. For
example, a value of 3 means "allow the maximum associated value to be
about 3 times larger than the number of input keys".
Conversely, a value of -3 means "allow the maximum associated value to
be about 3 times smaller than the number of input keys". Negative
values are useful for limiting the overall size of the generated hash
table, though this usually increases the number of duplicate hash
values.
If `generate switch' option <SAMP>`-S'</SAMP> is <EM>not</EM> enabled, the maximum
associated value influences the static array table size, and a larger
table should decrease the time required for an unsuccessful search, at
the expense of extra table space.
The default value is 1, thus the default maximum associated value about
the same size as the number of keys (for efficiency, the maximum
associated value is always rounded up to a power of 2). The actual
table size may vary somewhat, since this technique is essentially a
heuristic. In particular, setting this value too high slows down
<CODE>gperf</CODE>'s runtime, since it must search through a much larger range
of values. Judicious use of the <SAMP>`-f'</SAMP> option helps alleviate this
overhead, however.
</DL>
<H2><A NAME="SEC19" HREF="gperf_toc.html#TOC19">4.5 Informative Output</A></H2>
<DL COMPACT>
<DT><SAMP>`-h'</SAMP>
<DD>
<DT><SAMP>`--help'</SAMP>
<DD>
Prints a short summary on the meaning of each program option. Aborts
further program execution.
<DT><SAMP>`-v'</SAMP>
<DD>
<DT><SAMP>`--version'</SAMP>
<DD>
Prints out the current version number.
<DT><SAMP>`-d'</SAMP>
<DD>
<DT><SAMP>`--debug'</SAMP>
<DD>
Enables the debugging option. This produces verbose diagnostics to
"standard error" when <CODE>gperf</CODE> is executing. It is useful both for
maintaining the program and for determining whether a given set of
options is actually speeding up the search for a solution. Some useful
information is dumped at the end of the program when the <SAMP>`-d'</SAMP>
option is enabled.
</DL>
</P>
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<H1><A NAME="SEC14" HREF="gperf_toc.html#TOC14">4 Options to the <CODE>gperf</CODE> Utility</A></H1> <H1><A NAME="SEC20" HREF="gperf_toc.html#TOC20">5 Known Bugs and Limitations with <CODE>gperf</CODE></A></H1>
<P> <P>
There are <EM>many</EM> options to <CODE>gperf</CODE>. They were added to make The following are some limitations with the current release of
the program more convenient for use with real applications. "On-line" <CODE>gperf</CODE>:
help is readily available via the <SAMP>`-h'</SAMP> option. Here is the complete
list of options.
</P> </P>
<H2><A NAME="SEC15" HREF="gperf_toc.html#TOC15">4.1 Options that affect Interpretation of the Input File</A></H2>
<UL>
<DL COMPACT>
<DT><SAMP>`-e <VAR>keyword delimiter list</VAR>'</SAMP>
<DD>
Allows the user to provide a string containing delimiters used to
separate keywords from their attributes. The default is ",\n". This
option is essential if you want to use keywords that have embedded
commas or newlines. One useful trick is to use -e'TAB', where TAB is
the literal tab character.
<DT><SAMP>`-t'</SAMP>
<DD>
Allows you to include a <CODE>struct</CODE> type declaration for generated
code. Any text before a pair of consecutive %% is consider part of the
type declaration. Key words and additional fields may follow this, one
group of fields per line. A set of examples for generating perfect hash
tables and functions for Ada, C, and G++, Pascal, and Modula 2 and 3
reserved words are distributed with this release.
</DL>
</UL>
<H2><A NAME="SEC16" HREF="gperf_toc.html#TOC16">4.2 Options to specify the Language for the Output Code</A></H2>
<UL>
<DL COMPACT>
<DT><SAMP>`-L <VAR>generated language name</VAR>'</SAMP>
<DD>
Instructs <CODE>gperf</CODE> to generate code in the language specified by the
option's argument. Languages handled are currently:
<UL>
<DL COMPACT>
<DT><SAMP>`KR-C'</SAMP>
<DD>
Old-style K&#38;R C. This language is understood by old-style C compilers and
ANSI C compilers, but ANSI C compilers may flag warnings (or even errors)
because of lacking <SAMP>`const'</SAMP>.
<DT><SAMP>`C'</SAMP>
<DD>
Common C. This language is understood by ANSI C compilers, and also by
old-style C compilers, provided that you <CODE>#define const</CODE> to empty
for compilers which don't know about this keyword.
<DT><SAMP>`ANSI-C'</SAMP>
<DD>
ANSI C. This language is understood by ANSI C compilers and C++ compilers.
<DT><SAMP>`C++'</SAMP>
<DD>
C++. This language is understood by C++ compilers.
</DL>
</UL>
The default is C.
<DT><SAMP>`-a'</SAMP>
<DD>
This option is supported for compatibility with previous releases of
<CODE>gperf</CODE>. It does not do anything.
<DT><SAMP>`-g'</SAMP>
<DD>
This option is supported for compatibility with previous releases of
<CODE>gperf</CODE>. It does not do anything.
</DL>
</UL>
<H2><A NAME="SEC17" HREF="gperf_toc.html#TOC17">4.3 Options for fine tuning Details in the Output Code</A></H2>
<UL>
<DL COMPACT>
<DT><SAMP>`-K <VAR>key name</VAR>'</SAMP>
<DD>
This option is only useful when option <SAMP>`-t'</SAMP> has been given.
By default, the program assumes the structure component identifier for
the keyword is <SAMP>`name'</SAMP>. This option allows an arbitrary choice of
identifier for this component, although it still must occur as the first
field in your supplied <CODE>struct</CODE>.
<DT><SAMP>`-H <VAR>hash function name</VAR>'</SAMP>
<DD>
Allows you to specify the name for the generated hash function. Default
name is <SAMP>`hash'</SAMP>. This option permits the use of two hash tables in the
same file.
<DT><SAMP>`-N <VAR>lookup function name</VAR>'</SAMP>
<DD>
Allows you to specify the name for the generated lookup function.
Default name is <SAMP>`in_word_set'</SAMP>. This option permits completely automatic
generation of perfect hash functions, especially when multiple generated
hash functions are used in the same application.
<DT><SAMP>`-Z <VAR>class name</VAR>'</SAMP>
<DD>
This option is only useful when option <SAMP>`-L C++'</SAMP> has been given.
It allows you to specify the name of generated C++ class. Default name is
<CODE>Perfect_Hash</CODE>.
<DT><SAMP>`-7'</SAMP>
<DD>
This option specifies that all strings that will be passed as arguments
to the generated hash function and the generated lookup function will
solely consist of 7-bit ASCII characters (characters in the range 0..127).
(Note that the ANSI C functions <CODE>isalnum</CODE> and <CODE>isgraph</CODE> do
<EM>not</EM> guarantee that a character is in this range. Only an explicit
test like <SAMP>`c &#62;= 'A' &#38;&#38; c &#60;= 'Z''</SAMP> guarantees this.) This was the
default in earlier versions of <CODE>gperf</CODE>; now the default is to assume
8-bit characters.
<DT><SAMP>`-c'</SAMP>
<DD>
Generates C code that uses the <CODE>strncmp</CODE> function to perform
string comparisons. The default action is to use <CODE>strcmp</CODE>.
<DT><SAMP>`-C'</SAMP>
<DD>
Makes the contents of all generated lookup tables constant, i.e.,
"readonly". Many compilers can generate more efficient code for this
by putting the tables in readonly memory.
<DT><SAMP>`-E'</SAMP>
<DD>
Define constant values using an enum local to the lookup function rather
than with #defines. This also means that different lookup functions can
reside in the same file. Thanks to James Clark <CODE>&#60;jjc@ai.mit.edu&#62;</CODE>.
<DT><SAMP>`-I'</SAMP>
<DD>
Include the necessary system include file, <CODE>&#60;string.h&#62;</CODE>, at the
beginning of the code. By default, this is not done; the user must
include this header file himself to allow compilation of the code.
<DT><SAMP>`-G'</SAMP>
<DD>
Generate the static table of keywords as a static global variable,
rather than hiding it inside of the lookup function (which is the
default behavior).
<DT><SAMP>`-W <VAR>hash table array name</VAR>'</SAMP>
<DD>
Allows you to specify the name for the generated array containing the
hash table. Default name is <SAMP>`wordlist'</SAMP>. This option permits the
use of two hash tables in the same file, even when the option <SAMP>`-G'</SAMP>
is given.
<DT><SAMP>`-S <VAR>total switch statements</VAR>'</SAMP>
<DD>
Causes the generated C code to use a <CODE>switch</CODE> statement scheme,
rather than an array lookup table. This can lead to a reduction in both
time and space requirements for some keyfiles. The argument to this
option determines how many <CODE>switch</CODE> statements are generated. A
value of 1 generates 1 <CODE>switch</CODE> containing all the elements, a
value of 2 generates 2 tables with 1/2 the elements in each
<CODE>switch</CODE>, etc. This is useful since many C compilers cannot
correctly generate code for large <CODE>switch</CODE> statements. This option
was inspired in part by Keith Bostic's original C program.
<DT><SAMP>`-T'</SAMP>
<DD>
Prevents the transfer of the type declaration to the output file. Use
this option if the type is already defined elsewhere.
<DT><SAMP>`-p'</SAMP>
<DD>
This option is supported for compatibility with previous releases of
<CODE>gperf</CODE>. It does not do anything.
</DL>
</UL>
<H2><A NAME="SEC18" HREF="gperf_toc.html#TOC18">4.4 Options for changing the Algorithms employed by <CODE>gperf</CODE></A></H2>
<UL>
<DL COMPACT>
<DT><SAMP>`-k <VAR>keys</VAR>'</SAMP>
<DD>
Allows selection of the character key positions used in the keywords'
hash function. The allowable choices range between 1-126, inclusive.
The positions are separated by commas, e.g., <SAMP>`-k 9,4,13,14'</SAMP>;
ranges may be used, e.g., <SAMP>`-k 2-7'</SAMP>; and positions may occur
in any order. Furthermore, the meta-character '*' causes the generated
hash function to consider <STRONG>all</STRONG> character positions in each key,
whereas '$' instructs the hash function to use the "final character"
of a key (this is the only way to use a character position greater than
126, incidentally).
For instance, the option <SAMP>`-k 1,2,4,6-10,'$''</SAMP> generates a hash
function that considers positions 1,2,4,6,7,8,9,10, plus the last
character in each key (which may differ for each key, obviously). Keys
with length less than the indicated key positions work properly, since
selected key positions exceeding the key length are simply not
referenced in the hash function.
<DT><SAMP>`-l'</SAMP>
<DD>
Compare key lengths before trying a string comparison. This might cut
down on the number of string comparisons made during the lookup, since
keys with different lengths are never compared via <CODE>strcmp</CODE>.
However, using <SAMP>`-l'</SAMP> might greatly increase the size of the
generated C code if the lookup table range is large (which implies that
the switch option <SAMP>`-S'</SAMP> is not enabled), since the length table
contains as many elements as there are entries in the lookup table.
<DT><SAMP>`-D'</SAMP>
<DD>
Handle keywords whose key position sets hash to duplicate values.
Duplicate hash values occur for two reasons:
<UL> <UL>
<LI> <LI>
Since <CODE>gperf</CODE> does not backtrack it is possible for it to process The <CODE>gperf</CODE> utility is tuned to execute quickly, and works quickly
all your input keywords without finding a unique mapping for each word. for small to medium size data sets (around 1000 keywords). It is
However, frequently only a very small number of duplicates occur, and extremely useful for maintaining perfect hash functions for compiler
the majority of keys still require one probe into the table. keyword sets. Several recent enhancements now enable <CODE>gperf</CODE> to
work efficiently on much larger keyword sets (over 15,000 keywords).
When processing large keyword sets it helps greatly to have over 8 megs
of RAM.
However, since <CODE>gperf</CODE> does not backtrack no guaranteed solution
occurs on every run. On the other hand, it is usually easy to obtain a
solution by varying the option parameters. In particular, try the
<SAMP>`-r'</SAMP> option, and also try changing the default arguments to the
<SAMP>`-s'</SAMP> and <SAMP>`-j'</SAMP> options. To <EM>guarantee</EM> a solution, use
the <SAMP>`-D'</SAMP> and <SAMP>`-S'</SAMP> options, although the final results are not
likely to be a <EM>perfect</EM> hash function anymore! Finally, use the
<SAMP>`-f'</SAMP> option if you want <CODE>gperf</CODE> to generate the perfect hash
function <EM>fast</EM>, with less emphasis on making it minimal.
<LI> <LI>
Sometimes a set of keys may have the same names, but possess different The size of the generate static keyword array can get <EM>extremely</EM>
attributes. With the -D option <CODE>gperf</CODE> treats all these keys as part of large if the input keyword file is large or if the keywords are quite
an equivalence class and generates a perfect hash function with multiple similar. This tends to slow down the compilation of the generated C
comparisons for duplicate keys. It is up to you to completely code, and <EM>greatly</EM> inflates the object code size. If this
disambiguate the keywords by modifying the generated C code. However, situation occurs, consider using the <SAMP>`-S'</SAMP> option to reduce data
<CODE>gperf</CODE> helps you out by organizing the output. size, potentially increasing keyword recognition time a negligible
</UL> amount. Since many C compilers cannot correctly generated code for
large switch statements it is important to qualify the <VAR>-S</VAR> option
with an appropriate numerical argument that controls the number of
switch statements generated.
Option <SAMP>`-D'</SAMP> is extremely useful for certain large or highly <LI>
redundant keyword sets, e.g., assembler instruction opcodes.
Using this option usually means that the generated hash function is no
longer perfect. On the other hand, it permits <CODE>gperf</CODE> to work on
keyword sets that it otherwise could not handle.
<DT><SAMP>`-f <VAR>iteration amount</VAR>'</SAMP> The maximum number of key positions selected for a given key has an
<DD> arbitrary limit of 126. This restriction should be removed, and if
Generate the perfect hash function "fast". This decreases <CODE>gperf</CODE>'s anyone considers this a problem write me and let me know so I can remove
running time at the cost of minimizing generated table-size. The the constraint.
iteration amount represents the number of times to iterate when
resolving a collision. `0' means iterate by the number of keywords.
This option is probably most useful when used in conjunction with options
<SAMP>`-D'</SAMP> and/or <SAMP>`-S'</SAMP> for <EM>large</EM> keyword sets.
<DT><SAMP>`-i <VAR>initial value</VAR>'</SAMP>
<DD>
Provides an initial <VAR>value</VAR> for the associate values array. Default
is 0. Increasing the initial value helps inflate the final table size,
possibly leading to more time efficient keyword lookups. Note that this
option is not particularly useful when <SAMP>`-S'</SAMP> is used. Also,
<SAMP>`-i'</SAMP> is overriden when the <SAMP>`-r'</SAMP> option is used.
<DT><SAMP>`-j <VAR>jump value</VAR>'</SAMP>
<DD>
Affects the "jump value", i.e., how far to advance the
associated character value upon collisions. <VAR>Jump value</VAR> is rounded
up to an odd number, the default is 5. If the <VAR>jump value</VAR> is 0
<CODE>gperf</CODE> jumps by random amounts.
<DT><SAMP>`-n'</SAMP>
<DD>
Instructs the generator not to include the length of a keyword when
computing its hash value. This may save a few assembly instructions in
the generated lookup table.
<DT><SAMP>`-o'</SAMP>
<DD>
Reorders the keywords by sorting the keywords so that frequently
occuring key position set components appear first. A second reordering
pass follows so that keys with "already determined values" are placed
towards the front of the keylist. This may decrease the time required
to generate a perfect hash function for many keyword sets, and also
produce more minimal perfect hash functions. The reason for this is
that the reordering helps prune the search time by handling inevitable
collisions early in the search process. On the other hand, if the
number of keywords is <EM>very</EM> large using <SAMP>`-o'</SAMP> may
<EM>increase</EM> <CODE>gperf</CODE>'s execution time, since collisions will begin
earlier and continue throughout the remainder of keyword processing.
See Cichelli's paper from the January 1980 Communications of the ACM for
details.
<DT><SAMP>`-r'</SAMP>
<DD>
Utilizes randomness to initialize the associated values table. This
frequently generates solutions faster than using deterministic
initialization (which starts all associated values at 0). Furthermore,
using the randomization option generally increases the size of the
table. If <CODE>gperf</CODE> has difficultly with a certain keyword set try using
<SAMP>`-r'</SAMP> or <SAMP>`-D'</SAMP>.
<DT><SAMP>`-s <VAR>size-multiple</VAR>'</SAMP>
<DD>
Affects the size of the generated hash table. The numeric argument for
this option indicates "how many times larger or smaller" the maximum
associated value range should be, in relationship to the number of keys.
If the <VAR>size-multiple</VAR> is negative the maximum associated value is
calculated by <EM>dividing</EM> it into the total number of keys. For
example, a value of 3 means "allow the maximum associated value to be
about 3 times larger than the number of input keys".
Conversely, a value of -3 means "allow the maximum associated value to
be about 3 times smaller than the number of input keys". Negative
values are useful for limiting the overall size of the generated hash
table, though this usually increases the number of duplicate hash
values.
If `generate switch' option <SAMP>`-S'</SAMP> is <EM>not</EM> enabled, the maximum
associated value influences the static array table size, and a larger
table should decrease the time required for an unsuccessful search, at
the expense of extra table space.
The default value is 1, thus the default maximum associated value about
the same size as the number of keys (for efficiency, the maximum
associated value is always rounded up to a power of 2). The actual
table size may vary somewhat, since this technique is essentially a
heuristic. In particular, setting this value too high slows down
<CODE>gperf</CODE>'s runtime, since it must search through a much larger range
of values. Judicious use of the <SAMP>`-f'</SAMP> option helps alleviate this
overhead, however.
</DL>
</UL>
<H2><A NAME="SEC19" HREF="gperf_toc.html#TOC19">4.5 Informative Output</A></H2>
<UL>
<DL COMPACT>
<DT><SAMP>`-h'</SAMP>
<DD>
Prints a short summary on the meaning of each program option. Aborts
further program execution.
<DT><SAMP>`-v'</SAMP>
<DD>
Prints out the current version number.
<DT><SAMP>`-d'</SAMP>
<DD>
Enables the debugging option. This produces verbose diagnostics to
"standard error" when <CODE>gperf</CODE> is executing. It is useful both for
maintaining the program and for determining whether a given set of
options is actually speeding up the search for a solution. Some useful
information is dumped at the end of the program when the <SAMP>`-d'</SAMP>
option is enabled.
</DL>
</UL> </UL>
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</HEAD> </HEAD>
<BODY> <BODY>
Go to the <A HREF="gperf_1.html">first</A>, <A HREF="gperf_7.html">previous</A>, <A HREF="gperf_9.html">next</A>, <A HREF="gperf_11.html">last</A> section, <A HREF="gperf_toc.html">table of contents</A>. Go to the <A HREF="gperf_1.html">first</A>, <A HREF="gperf_7.html">previous</A>, <A HREF="gperf_9.html">next</A>, <A HREF="gperf_11.html">last</A> section, <A HREF="gperf_toc.html">table of contents</A>.
<P><HR><P> <P><HR><P>
<H1><A NAME="SEC20" HREF="gperf_toc.html#TOC20">5 Known Bugs and Limitations with <CODE>gperf</CODE></A></H1> <H1><A NAME="SEC21" HREF="gperf_toc.html#TOC21">6 Things Still Left to Do</A></H1>
<P> <P>
The following are some limitations with the current release of It should be "relatively" easy to replace the current perfect hash
<CODE>gperf</CODE>: function algorithm with a more exhaustive approach; the perfect hash
module is essential independent from other program modules. Additional
worthwhile improvements include:
</P> </P>
<UL> <UL>
<LI> <LI>
The <CODE>gperf</CODE> utility is tuned to execute quickly, and works quickly Make the algorithm more robust. At present, the program halts with an
for small to medium size data sets (around 1000 keywords). It is error diagnostic if it can't find a direct solution and the <SAMP>`-D'</SAMP>
extremely useful for maintaining perfect hash functions for compiler option is not enabled. A more comprehensive, albeit computationally
keyword sets. Several recent enhancements now enable <CODE>gperf</CODE> to expensive, approach would employ backtracking or enable alternative
work efficiently on much larger keyword sets (over 15,000 keywords). options and retry. It's not clear how helpful this would be, in
When processing large keyword sets it helps greatly to have over 8 megs general, since most search sets are rather small in practice.
of RAM.
However, since <CODE>gperf</CODE> does not backtrack no guaranteed solution
occurs on every run. On the other hand, it is usually easy to obtain a
solution by varying the option parameters. In particular, try the
<SAMP>`-r'</SAMP> option, and also try changing the default arguments to the
<SAMP>`-s'</SAMP> and <SAMP>`-j'</SAMP> options. To <EM>guarantee</EM> a solution, use
the <SAMP>`-D'</SAMP> and <SAMP>`-S'</SAMP> options, although the final results are not
likely to be a <EM>perfect</EM> hash function anymore! Finally, use the
<SAMP>`-f'</SAMP> option if you want <CODE>gperf</CODE> to generate the perfect hash
function <EM>fast</EM>, with less emphasis on making it minimal.
<LI> <LI>
The size of the generate static keyword array can get <EM>extremely</EM> Another useful extension involves modifying the program to generate
large if the input keyword file is large or if the keywords are quite "minimal" perfect hash functions (under certain circumstances, the
similar. This tends to slow down the compilation of the generated C current version can be rather extravagant in the generated table size).
code, and <EM>greatly</EM> inflates the object code size. If this Again, this is mostly of theoretical interest, since a sparse table
situation occurs, consider using the <SAMP>`-S'</SAMP> option to reduce data often produces faster lookups, and use of the <SAMP>`-S'</SAMP> <CODE>switch</CODE>
size, potentially increasing keyword recognition time a negligible option can minimize the data size, at the expense of slightly longer
amount. Since many C compilers cannot correctly generated code for lookups (note that the gcc compiler generally produces good code for
large switch statements it is important to qualify the <VAR>-S</VAR> option <CODE>switch</CODE> statements, reducing the need for more complex schemes).
with an appropriate numerical argument that controls the number of
switch statements generated.
<LI> <LI>
The maximum number of key positions selected for a given key has an In addition to improving the algorithm, it would also be useful to
arbitrary limit of 126. This restriction should be removed, and if generate a C++ class or Ada package as the code output, in addition to
anyone considers this a problem write me and let me know so I can remove the current C routines.
the constraint.
</UL> </UL>
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<TITLE>User's Guide to gperf - 6 Things Still Left to Do</TITLE> <TITLE>Perfect Hash Function Generator - 7 Implementation Details of GNU gperf</TITLE>
</HEAD> </HEAD>
<BODY> <BODY>
Go to the <A HREF="gperf_1.html">first</A>, <A HREF="gperf_8.html">previous</A>, <A HREF="gperf_10.html">next</A>, <A HREF="gperf_11.html">last</A> section, <A HREF="gperf_toc.html">table of contents</A>. Go to the <A HREF="gperf_1.html">first</A>, <A HREF="gperf_8.html">previous</A>, <A HREF="gperf_10.html">next</A>, <A HREF="gperf_11.html">last</A> section, <A HREF="gperf_toc.html">table of contents</A>.
<P><HR><P> <P><HR><P>
<H1><A NAME="SEC21" HREF="gperf_toc.html#TOC21">6 Things Still Left to Do</A></H1> <H1><A NAME="SEC22" HREF="gperf_toc.html#TOC22">7 Implementation Details of GNU <CODE>gperf</CODE></A></H1>
<P> <P>
It should be "relatively" easy to replace the current perfect hash A paper describing the high-level description of the data structures and
function algorithm with a more exhaustive approach; the perfect hash algorithms used to implement <CODE>gperf</CODE> will soon be available. This
module is essential independent from other program modules. Additional paper is useful not only from a maintenance and enhancement perspective,
worthwhile improvements include: but also because they demonstrate several clever and useful programming
techniques, e.g., `Iteration Number' boolean arrays, double
hashing, a "safe" and efficient method for reading arbitrarily long
input from a file, and a provably optimal algorithm for simultaneously
determining both the minimum and maximum elements in a list.
</P> </P>
<UL>
<LI>
Make the algorithm more robust. At present, the program halts with an
error diagnostic if it can't find a direct solution and the <SAMP>`-D'</SAMP>
option is not enabled. A more comprehensive, albeit computationally
expensive, approach would employ backtracking or enable alternative
options and retry. It's not clear how helpful this would be, in
general, since most search sets are rather small in practice.
<LI>
Another useful extension involves modifying the program to generate
"minimal" perfect hash functions (under certain circumstances, the
current version can be rather extravagant in the generated table size).
Again, this is mostly of theoretical interest, since a sparse table
often produces faster lookups, and use of the <SAMP>`-S'</SAMP> <CODE>switch</CODE>
option can minimize the data size, at the expense of slightly longer
lookups (note that the gcc compiler generally produces good code for
<CODE>switch</CODE> statements, reducing the need for more complex schemes).
<LI>
In addition to improving the algorithm, it would also be useful to
generate a C++ class or Ada package as the code output, in addition to
the current C routines.
</UL>
<P><HR><P> <P><HR><P>
Go to the <A HREF="gperf_1.html">first</A>, <A HREF="gperf_8.html">previous</A>, <A HREF="gperf_10.html">next</A>, <A HREF="gperf_11.html">last</A> section, <A HREF="gperf_toc.html">table of contents</A>. Go to the <A HREF="gperf_1.html">first</A>, <A HREF="gperf_8.html">previous</A>, <A HREF="gperf_10.html">next</A>, <A HREF="gperf_11.html">last</A> section, <A HREF="gperf_toc.html">table of contents</A>.
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<TITLE>User's Guide to gperf - Table of Contents</TITLE> <TITLE>Perfect Hash Function Generator - Table of Contents</TITLE>
</HEAD> </HEAD>
<BODY> <BODY>
<H1>User's Guide to <CODE>gperf</CODE></H1> <H1>User's Guide to <CODE>gperf</CODE> 2.7.2</H1>
<H2>The GNU Perfect Hash Function Generator</H2>
<H2>Edition 2.7.2, 20 August 2000</H2>
<ADDRESS>Douglas C. Schmidt</ADDRESS>
<P> <P>
<P><HR><P> <P><HR><P>
<UL> <UL>
<LI><A NAME="TOC1" HREF="gperf_1.html#SEC1">Introduction</A> <LI><A NAME="TOC1" HREF="gperf_1.html#SEC1">GNU GENERAL PUBLIC LICENSE</A>
<LI><A NAME="TOC2" HREF="gperf_2.html#SEC2">GNU GENERAL PUBLIC LICENSE</A>
<UL> <UL>
<LI><A NAME="TOC3" HREF="gperf_2.html#SEC3">Preamble</A> <LI><A NAME="TOC2" HREF="gperf_1.html#SEC2">Preamble</A>
<LI><A NAME="TOC4" HREF="gperf_2.html#SEC4">Appendix: How to Apply These Terms to Your New Programs</A> <LI><A NAME="TOC3" HREF="gperf_1.html#SEC3">How to Apply These Terms to Your New Programs</A>
</UL> </UL>
<LI><A NAME="TOC5" HREF="gperf_3.html#SEC5">Contributors to GNU <CODE>gperf</CODE> Utility</A> <LI><A NAME="TOC4" HREF="gperf_2.html#SEC4">Contributors to GNU <CODE>gperf</CODE> Utility</A>
<LI><A NAME="TOC6" HREF="gperf_4.html#SEC6">1 Introduction</A> <LI><A NAME="TOC5" HREF="gperf_3.html#SEC5">1 Introduction</A>
<LI><A NAME="TOC7" HREF="gperf_5.html#SEC7">2 Static search structures and GNU <CODE>gperf</CODE></A> <LI><A NAME="TOC6" HREF="gperf_4.html#SEC6">2 Static search structures and GNU <CODE>gperf</CODE></A>
<LI><A NAME="TOC8" HREF="gperf_6.html#SEC8">3 High-Level Description of GNU <CODE>gperf</CODE></A> <LI><A NAME="TOC7" HREF="gperf_5.html#SEC7">3 High-Level Description of GNU <CODE>gperf</CODE></A>
<UL> <UL>
<LI><A NAME="TOC9" HREF="gperf_6.html#SEC9">3.1 Input Format to <CODE>gperf</CODE></A> <LI><A NAME="TOC8" HREF="gperf_5.html#SEC8">3.1 Input Format to <CODE>gperf</CODE></A>
<UL> <UL>
<LI><A NAME="TOC10" HREF="gperf_6.html#SEC10">3.1.1 <CODE>struct</CODE> Declarations and C Code Inclusion</A> <LI><A NAME="TOC9" HREF="gperf_5.html#SEC9">3.1.1 <CODE>struct</CODE> Declarations and C Code Inclusion</A>
<LI><A NAME="TOC11" HREF="gperf_6.html#SEC11">3.1.2 Format for Keyword Entries</A> <LI><A NAME="TOC10" HREF="gperf_5.html#SEC10">3.1.2 Format for Keyword Entries</A>
<LI><A NAME="TOC12" HREF="gperf_6.html#SEC12">3.1.3 Including Additional C Functions</A> <LI><A NAME="TOC11" HREF="gperf_5.html#SEC11">3.1.3 Including Additional C Functions</A>
</UL> </UL>
<LI><A NAME="TOC13" HREF="gperf_6.html#SEC13">3.2 Output Format for Generated C Code with <CODE>gperf</CODE></A> <LI><A NAME="TOC12" HREF="gperf_5.html#SEC12">3.2 Output Format for Generated C Code with <CODE>gperf</CODE></A>
<LI><A NAME="TOC13" HREF="gperf_5.html#SEC13">3.3 Use of NUL characters</A>
</UL> </UL>
<LI><A NAME="TOC14" HREF="gperf_7.html#SEC14">4 Options to the <CODE>gperf</CODE> Utility</A> <LI><A NAME="TOC14" HREF="gperf_6.html#SEC14">4 Invoking <CODE>gperf</CODE></A>
<UL> <UL>
<LI><A NAME="TOC15" HREF="gperf_7.html#SEC15">4.1 Options that affect Interpretation of the Input File</A> <LI><A NAME="TOC15" HREF="gperf_6.html#SEC15">4.1 Options that affect Interpretation of the Input File</A>
<LI><A NAME="TOC16" HREF="gperf_7.html#SEC16">4.2 Options to specify the Language for the Output Code</A> <LI><A NAME="TOC16" HREF="gperf_6.html#SEC16">4.2 Options to specify the Language for the Output Code</A>
<LI><A NAME="TOC17" HREF="gperf_7.html#SEC17">4.3 Options for fine tuning Details in the Output Code</A> <LI><A NAME="TOC17" HREF="gperf_6.html#SEC17">4.3 Options for fine tuning Details in the Output Code</A>
<LI><A NAME="TOC18" HREF="gperf_7.html#SEC18">4.4 Options for changing the Algorithms employed by <CODE>gperf</CODE></A> <LI><A NAME="TOC18" HREF="gperf_6.html#SEC18">4.4 Options for changing the Algorithms employed by <CODE>gperf</CODE></A>
<LI><A NAME="TOC19" HREF="gperf_7.html#SEC19">4.5 Informative Output</A> <LI><A NAME="TOC19" HREF="gperf_6.html#SEC19">4.5 Informative Output</A>
</UL> </UL>
<LI><A NAME="TOC20" HREF="gperf_8.html#SEC20">5 Known Bugs and Limitations with <CODE>gperf</CODE></A> <LI><A NAME="TOC20" HREF="gperf_7.html#SEC20">5 Known Bugs and Limitations with <CODE>gperf</CODE></A>
<LI><A NAME="TOC21" HREF="gperf_9.html#SEC21">6 Things Still Left to Do</A> <LI><A NAME="TOC21" HREF="gperf_8.html#SEC21">6 Things Still Left to Do</A>
<LI><A NAME="TOC22" HREF="gperf_10.html#SEC22">7 Implementation Details of GNU <CODE>gperf</CODE></A> <LI><A NAME="TOC22" HREF="gperf_9.html#SEC22">7 Implementation Details of GNU <CODE>gperf</CODE></A>
<LI><A NAME="TOC23" HREF="gperf_11.html#SEC23">8 Bibliography</A> <LI><A NAME="TOC23" HREF="gperf_10.html#SEC23">8 Bibliography</A>
<LI><A NAME="TOC24" HREF="gperf_11.html#SEC24">Concept Index</A>
</UL> </UL>
<P><HR><P> <P><HR><P>
This document was generated on 15 April 1998 using the This document was generated on 20 August 2000 using the
<A HREF="http://wwwcn.cern.ch/dci/texi2html/">texi2html</A> <A HREF="http://wwwcn.cern.ch/dci/texi2html/">texi2html</A>
translator version 1.51.</P> translator version 1.51.</P>
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/* C code produced by gperf version 2.7 */ /* C code produced by gperf version 2.7.2 */
/* Command-line: ../src/gperf -L C -F ', 0, 0' -p -j1 -i 1 -g -o -t -G -N is_reserved_word -k'1,3,$' */ /* Command-line: ../src/gperf -L C -F ', 0, 0' -p -j1 -i 1 -g -o -t -G -N is_reserved_word -k'1,3,$' */
/* Command-line: gperf -L KR-C -F ', 0, 0' -p -j1 -i 1 -g -o -t -N is_reserved_word -k1,3,$ c-parse.gperf */ /* Command-line: gperf -L KR-C -F ', 0, 0' -p -j1 -i 1 -g -o -t -N is_reserved_word -k1,3,$ c-parse.gperf */
struct resword { const char *name; short token; enum rid rid; }; struct resword { const char *name; short token; enum rid rid; };
@@ -12,6 +12,10 @@ struct resword { const char *name; short token; enum rid rid; };
#ifdef __GNUC__ #ifdef __GNUC__
__inline __inline
#else
#ifdef __cplusplus
inline
#endif
#endif #endif
static unsigned int static unsigned int
hash (str, len) hash (str, len)

6
tests/chill.exp
View File

@@ -1,4 +1,4 @@
/* C code produced by gperf version 2.7 */ /* C code produced by gperf version 2.7.2 */
/* Command-line: ../src/gperf -L C -F ', 0, 0, 0' -D -E -S1 -p -j1 -i 1 -g -o -t -k'*' */ /* Command-line: ../src/gperf -L C -F ', 0, 0, 0' -D -E -S1 -p -j1 -i 1 -g -o -t -k'*' */
struct resword { struct resword {
const char *name; const char *name;
@@ -11,6 +11,10 @@ extern tree ridpointers [];
#ifdef __GNUC__ #ifdef __GNUC__
__inline __inline
#else
#ifdef __cplusplus
inline
#endif
#endif #endif
static unsigned int static unsigned int
hash (str, len) hash (str, len)

6
tests/cplusplus.exp
View File

@@ -1,4 +1,4 @@
/* C code produced by gperf version 2.7 */ /* C code produced by gperf version 2.7.2 */
/* Command-line: ../src/gperf -L C -F ', 0, 0' -p -j1 -g -o -t -N is_reserved_word -k'1,4,7,$' */ /* Command-line: ../src/gperf -L C -F ', 0, 0' -p -j1 -g -o -t -N is_reserved_word -k'1,4,7,$' */
/* Command-line: gperf -L KR-C -F ', 0, 0' -p -j1 -g -o -t -N is_reserved_word -k1,4,$,7 gplus.gperf */ /* Command-line: gperf -L KR-C -F ', 0, 0' -p -j1 -g -o -t -N is_reserved_word -k1,4,$,7 gplus.gperf */
struct resword { const char *name; short token; enum rid rid;}; struct resword { const char *name; short token; enum rid rid;};
@@ -12,6 +12,10 @@ struct resword { const char *name; short token; enum rid rid;};
#ifdef __GNUC__ #ifdef __GNUC__
__inline __inline
#else
#ifdef __cplusplus
inline
#endif
#endif #endif
static unsigned int static unsigned int
hash (str, len) hash (str, len)

6
tests/gpc.exp
View File

@@ -1,4 +1,4 @@
/* C code produced by gperf version 2.7 */ /* C code produced by gperf version 2.7.2 */
/* Command-line: ../src/gperf -g -o -j1 -t -p -N is_reserved_word */ /* Command-line: ../src/gperf -g -o -j1 -t -p -N is_reserved_word */
/* ISO Pascal 7185 reserved words. /* ISO Pascal 7185 reserved words.
* *
@@ -20,6 +20,10 @@ struct resword { char *name; short token; short iclass;};
#ifdef __GNUC__ #ifdef __GNUC__
__inline __inline
#else
#ifdef __cplusplus
inline
#endif
#endif #endif
static unsigned int static unsigned int
hash (str, len) hash (str, len)

6
tests/java.exp
View File

@@ -1,4 +1,4 @@
/* C code produced by gperf version 2.7 */ /* C code produced by gperf version 2.7.2 */
/* Command-line: ../src/gperf -L C -F ', 0' -p -t -j1 -i 1 -g -o -N java_keyword -k'1,3,$' */ /* Command-line: ../src/gperf -L C -F ', 0' -p -t -j1 -i 1 -g -o -N java_keyword -k'1,3,$' */
/* Keyword definition for the GNU compiler for the Java(TM) language. /* Keyword definition for the GNU compiler for the Java(TM) language.
Copyright (C) 1997, 1998 Free Software Foundation, Inc. Copyright (C) 1997, 1998 Free Software Foundation, Inc.
@@ -36,6 +36,10 @@ struct java_keyword { const char *name; int token; };
#ifdef __GNUC__ #ifdef __GNUC__
__inline __inline
#else
#ifdef __cplusplus
inline
#endif
#endif #endif
static unsigned int static unsigned int
hash (str, len) hash (str, len)

8
tests/modula2.exp
View File

@@ -1,4 +1,4 @@
/* C code produced by gperf version 2.7 */ /* C code produced by gperf version 2.7.2 */
/* Command-line: ../src/gperf -n -k1-8 -l */ /* Command-line: ../src/gperf -n -k1-8 -l */
#define TOTAL_KEYWORDS 40 #define TOTAL_KEYWORDS 40
@@ -10,6 +10,10 @@
#ifdef __GNUC__ #ifdef __GNUC__
__inline __inline
#else
#ifdef __cplusplus
inline
#endif
#endif #endif
static unsigned int static unsigned int
hash (str, len) hash (str, len)
@@ -194,7 +198,7 @@ in_word_set (str, len)
{ {
register const char *s = wordlist[key]; register const char *s = wordlist[key];
if (*str == *s && !strcmp (str + 1, s + 1)) if (*str == *s && !memcmp (str + 1, s + 1, len - 1))
return s; return s;
} }
} }

6
tests/objc.exp
View File

@@ -1,4 +1,4 @@
/* C code produced by gperf version 2.7 */ /* C code produced by gperf version 2.7.2 */
/* Command-line: ../src/gperf -p -j1 -i 1 -g -o -t -N is_reserved_word -k'1,3,$' */ /* Command-line: ../src/gperf -p -j1 -i 1 -g -o -t -N is_reserved_word -k'1,3,$' */
/* Command-line: gperf -p -j1 -i 1 -g -o -t -N is_reserved_word -k1,3,$ objc.gperf */ /* Command-line: gperf -p -j1 -i 1 -g -o -t -N is_reserved_word -k1,3,$ objc.gperf */
struct resword { char *name; short token; enum rid rid; }; struct resword { char *name; short token; enum rid rid; };
@@ -12,6 +12,10 @@ struct resword { char *name; short token; enum rid rid; };
#ifdef __GNUC__ #ifdef __GNUC__
__inline __inline
#else
#ifdef __cplusplus
inline
#endif
#endif #endif
static unsigned int static unsigned int
hash (str, len) hash (str, len)

6
tests/test-4.exp
View File

@@ -1,4 +1,4 @@
/* C code produced by gperf version 2.7 */ /* C code produced by gperf version 2.7.2 */
/* Command-line: ../src/gperf -D -p -t */ /* Command-line: ../src/gperf -D -p -t */
/* Command-line: gperf -L KR-C -F ', 0, 0' -p -j1 -i 1 -g -o -t -N is_reserved_word -k1,3,$ c-parse.gperf */ /* Command-line: gperf -L KR-C -F ', 0, 0' -p -j1 -i 1 -g -o -t -N is_reserved_word -k1,3,$ c-parse.gperf */
struct resword { const char *name; short token; enum rid rid; }; struct resword { const char *name; short token; enum rid rid; };
@@ -12,6 +12,10 @@ struct resword { const char *name; short token; enum rid rid; };
#ifdef __GNUC__ #ifdef __GNUC__
__inline __inline
#else
#ifdef __cplusplus
inline
#endif
#endif #endif
static unsigned int static unsigned int
hash (str, len) hash (str, len)