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<!-- This HTML file has been created by texi2html 1.52
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from gperf.texi on 13 January 2006 -->
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<TITLE>Perfect Hash Function Generator</TITLE>
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</HEAD>
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<BODY>
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<H1>User's Guide to <CODE>gperf</CODE> 3.0.2</H1>
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<H2>The GNU Perfect Hash Function Generator</H2>
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<H2>Edition 3.0.2, 13 January 2006</H2>
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<ADDRESS>Douglas C. Schmidt</ADDRESS>
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<ADDRESS>Bruno Haible</ADDRESS>
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<P>
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<P><HR><P>
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<H1>Table of Contents</H1>
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<UL>
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<LI><A NAME="TOC1" HREF="gperf.html#SEC1">GNU GENERAL PUBLIC LICENSE</A>
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<UL>
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<LI><A NAME="TOC2" HREF="gperf.html#SEC2">Preamble</A>
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<LI><A NAME="TOC3" HREF="gperf.html#SEC3">How to Apply These Terms to Your New Programs</A>
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</UL>
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<LI><A NAME="TOC4" HREF="gperf.html#SEC4">Contributors to GNU <CODE>gperf</CODE> Utility</A>
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<LI><A NAME="TOC5" HREF="gperf.html#SEC5">1 Introduction</A>
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<LI><A NAME="TOC6" HREF="gperf.html#SEC6">2 Static search structures and GNU <CODE>gperf</CODE></A>
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<LI><A NAME="TOC7" HREF="gperf.html#SEC7">3 High-Level Description of GNU <CODE>gperf</CODE></A>
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<UL>
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<LI><A NAME="TOC8" HREF="gperf.html#SEC8">3.1 Input Format to <CODE>gperf</CODE></A>
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<UL>
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<LI><A NAME="TOC9" HREF="gperf.html#SEC9">3.1.1 Declarations</A>
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<UL>
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<LI><A NAME="TOC10" HREF="gperf.html#SEC10">3.1.1.1 User-supplied <CODE>struct</CODE></A>
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<LI><A NAME="TOC11" HREF="gperf.html#SEC11">3.1.1.2 Gperf Declarations</A>
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<LI><A NAME="TOC12" HREF="gperf.html#SEC12">3.1.1.3 C Code Inclusion</A>
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</UL>
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<LI><A NAME="TOC13" HREF="gperf.html#SEC13">3.1.2 Format for Keyword Entries</A>
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<LI><A NAME="TOC14" HREF="gperf.html#SEC14">3.1.3 Including Additional C Functions</A>
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<LI><A NAME="TOC15" HREF="gperf.html#SEC15">3.1.4 Where to place directives for GNU <CODE>indent</CODE>.</A>
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</UL>
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<LI><A NAME="TOC16" HREF="gperf.html#SEC16">3.2 Output Format for Generated C Code with <CODE>gperf</CODE></A>
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<LI><A NAME="TOC17" HREF="gperf.html#SEC17">3.3 Use of NUL bytes</A>
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</UL>
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<LI><A NAME="TOC18" HREF="gperf.html#SEC18">4 Invoking <CODE>gperf</CODE></A>
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<UL>
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<LI><A NAME="TOC19" HREF="gperf.html#SEC19">4.1 Specifying the Location of the Output File</A>
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<LI><A NAME="TOC20" HREF="gperf.html#SEC20">4.2 Options that affect Interpretation of the Input File</A>
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<LI><A NAME="TOC21" HREF="gperf.html#SEC21">4.3 Options to specify the Language for the Output Code</A>
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<LI><A NAME="TOC22" HREF="gperf.html#SEC22">4.4 Options for fine tuning Details in the Output Code</A>
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<LI><A NAME="TOC23" HREF="gperf.html#SEC23">4.5 Options for changing the Algorithms employed by <CODE>gperf</CODE></A>
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<LI><A NAME="TOC24" HREF="gperf.html#SEC24">4.6 Informative Output</A>
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</UL>
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<LI><A NAME="TOC25" HREF="gperf.html#SEC25">5 Known Bugs and Limitations with <CODE>gperf</CODE></A>
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<LI><A NAME="TOC26" HREF="gperf.html#SEC26">6 Things Still Left to Do</A>
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<LI><A NAME="TOC27" HREF="gperf.html#SEC27">7 Bibliography</A>
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<LI><A NAME="TOC28" HREF="gperf.html#SEC28">Concept Index</A>
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</UL>
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<P><HR><P>
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<H1><A NAME="SEC1" HREF="gperf.html#TOC1">GNU GENERAL PUBLIC LICENSE</A></H1>
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<P>
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Version 2, June 1991
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</P>
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<PRE>
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Copyright (C) 1989, 1991 Free Software Foundation, Inc.,
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59 Temple Place, Suite 330, Boston, MA 02111-1307, USA.
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Everyone is permitted to copy and distribute verbatim copies
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of this license document, but changing it is not allowed.
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</PRE>
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<H2><A NAME="SEC2" HREF="gperf.html#TOC2">Preamble</A></H2>
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<P>
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The licenses for most software are designed to take away your
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freedom to share and change it. By contrast, the GNU General Public
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License is intended to guarantee your freedom to share and change free
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software--to make sure the software is free for all its users. This
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General Public License applies to most of the Free Software
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Foundation's software and to any other program whose authors commit to
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using it. (Some other Free Software Foundation software is covered by
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the GNU Library General Public License instead.) You can apply it to
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your programs, too.
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</P>
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<P>
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When we speak of free software, we are referring to freedom, not
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price. Our General Public Licenses are designed to make sure that you
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have the freedom to distribute copies of free software (and charge for
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this service if you wish), that you receive source code or can get it
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if you want it, that you can change the software or use pieces of it
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in new free programs; and that you know you can do these things.
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</P>
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<P>
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To protect your rights, we need to make restrictions that forbid
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anyone to deny you these rights or to ask you to surrender the rights.
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These restrictions translate to certain responsibilities for you if you
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distribute copies of the software, or if you modify it.
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</P>
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<P>
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For example, if you distribute copies of such a program, whether
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gratis or for a fee, you must give the recipients all the rights that
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you have. You must make sure that they, too, receive or can get the
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source code. And you must show them these terms so they know their
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rights.
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</P>
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<P>
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We protect your rights with two steps: (1) copyright the software, and
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(2) offer you this license which gives you legal permission to copy,
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distribute and/or modify the software.
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</P>
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<P>
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Also, for each author's protection and ours, we want to make certain
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that everyone understands that there is no warranty for this free
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software. If the software is modified by someone else and passed on, we
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want its recipients to know that what they have is not the original, so
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that any problems introduced by others will not reflect on the original
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authors' reputations.
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</P>
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<P>
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Finally, any free program is threatened constantly by software
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patents. We wish to avoid the danger that redistributors of a free
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program will individually obtain patent licenses, in effect making the
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program proprietary. To prevent this, we have made it clear that any
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patent must be licensed for everyone's free use or not licensed at all.
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</P>
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<P>
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The precise terms and conditions for copying, distribution and
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modification follow.
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</P>
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<P>
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TERMS AND CONDITIONS FOR COPYING, DISTRIBUTION AND MODIFICATION
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</P>
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<OL>
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<LI>
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This License applies to any program or other work which contains
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a notice placed by the copyright holder saying it may be distributed
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under the terms of this General Public License. The "Program", below,
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refers to any such program or work, and a "work based on the Program"
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means either the Program or any derivative work under copyright law:
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that is to say, a work containing the Program or a portion of it,
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either verbatim or with modifications and/or translated into another
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language. (Hereinafter, translation is included without limitation in
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the term "modification".) Each licensee is addressed as "you".
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Activities other than copying, distribution and modification are not
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covered by this License; they are outside its scope. The act of
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running the Program is not restricted, and the output from the Program
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is covered only if its contents constitute a work based on the
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Program (independent of having been made by running the Program).
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Whether that is true depends on what the Program does.
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<LI>
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You may copy and distribute verbatim copies of the Program's
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source code as you receive it, in any medium, provided that you
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conspicuously and appropriately publish on each copy an appropriate
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copyright notice and disclaimer of warranty; keep intact all the
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notices that refer to this License and to the absence of any warranty;
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and give any other recipients of the Program a copy of this License
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along with the Program.
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You may charge a fee for the physical act of transferring a copy, and
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you may at your option offer warranty protection in exchange for a fee.
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<LI>
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You may modify your copy or copies of the Program or any portion
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of it, thus forming a work based on the Program, and copy and
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distribute such modifications or work under the terms of Section 1
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above, provided that you also meet all of these conditions:
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<OL>
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<LI>
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You must cause the modified files to carry prominent notices
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stating that you changed the files and the date of any change.
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You must cause any work that you distribute or publish, that in
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whole or in part contains or is derived from the Program or any
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part thereof, to be licensed as a whole at no charge to all third
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parties under the terms of this License.
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<LI>
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If the modified program normally reads commands interactively
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when run, you must cause it, when started running for such
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interactive use in the most ordinary way, to print or display an
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announcement including an appropriate copyright notice and a
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notice that there is no warranty (or else, saying that you provide
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a warranty) and that users may redistribute the program under
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these conditions, and telling the user how to view a copy of this
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License. (Exception: if the Program itself is interactive but
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does not normally print such an announcement, your work based on
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the Program is not required to print an announcement.)
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</OL>
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These requirements apply to the modified work as a whole. If
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identifiable sections of that work are not derived from the Program,
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and can be reasonably considered independent and separate works in
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themselves, then this License, and its terms, do not apply to those
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sections when you distribute them as separate works. But when you
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distribute the same sections as part of a whole which is a work based
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on the Program, the distribution of the whole must be on the terms of
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this License, whose permissions for other licensees extend to the
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entire whole, and thus to each and every part regardless of who wrote it.
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Thus, it is not the intent of this section to claim rights or contest
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your rights to work written entirely by you; rather, the intent is to
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exercise the right to control the distribution of derivative or
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collective works based on the Program.
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In addition, mere aggregation of another work not based on the Program
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with the Program (or with a work based on the Program) on a volume of
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a storage or distribution medium does not bring the other work under
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the scope of this License.
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<LI>
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You may copy and distribute the Program (or a work based on it,
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under Section 2) in object code or executable form under the terms of
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Sections 1 and 2 above provided that you also do one of the following:
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<OL>
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<LI>
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Accompany it with the complete corresponding machine-readable
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source code, which must be distributed under the terms of Sections
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1 and 2 above on a medium customarily used for software interchange; or,
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<LI>
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Accompany it with a written offer, valid for at least three
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years, to give any third party, for a charge no more than your
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cost of physically performing source distribution, a complete
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machine-readable copy of the corresponding source code, to be
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distributed under the terms of Sections 1 and 2 above on a medium
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customarily used for software interchange; or,
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<LI>
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Accompany it with the information you received as to the offer
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to distribute corresponding source code. (This alternative is
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allowed only for noncommercial distribution and only if you
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received the program in object code or executable form with such
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an offer, in accord with Subsection b above.)
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</OL>
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The source code for a work means the preferred form of the work for
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making modifications to it. For an executable work, complete source
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code means all the source code for all modules it contains, plus any
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associated interface definition files, plus the scripts used to
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control compilation and installation of the executable. However, as a
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special exception, the source code distributed need not include
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anything that is normally distributed (in either source or binary
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form) with the major components (compiler, kernel, and so on) of the
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operating system on which the executable runs, unless that component
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itself accompanies the executable.
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If distribution of executable or object code is made by offering
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access to copy from a designated place, then offering equivalent
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access to copy the source code from the same place counts as
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distribution of the source code, even though third parties are not
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compelled to copy the source along with the object code.
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<LI>
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You may not copy, modify, sublicense, or distribute the Program
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except as expressly provided under this License. Any attempt
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otherwise to copy, modify, sublicense or distribute the Program is
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void, and will automatically terminate your rights under this License.
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However, parties who have received copies, or rights, from you under
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this License will not have their licenses terminated so long as such
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parties remain in full compliance.
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<LI>
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You are not required to accept this License, since you have not
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signed it. However, nothing else grants you permission to modify or
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distribute the Program or its derivative works. These actions are
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prohibited by law if you do not accept this License. Therefore, by
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modifying or distributing the Program (or any work based on the
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Program), you indicate your acceptance of this License to do so, and
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all its terms and conditions for copying, distributing or modifying
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the Program or works based on it.
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<LI>
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Each time you redistribute the Program (or any work based on the
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Program), the recipient automatically receives a license from the
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original licensor to copy, distribute or modify the Program subject to
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these terms and conditions. You may not impose any further
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restrictions on the recipients' exercise of the rights granted herein.
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You are not responsible for enforcing compliance by third parties to
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this License.
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<LI>
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If, as a consequence of a court judgment or allegation of patent
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infringement or for any other reason (not limited to patent issues),
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conditions are imposed on you (whether by court order, agreement or
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otherwise) that contradict the conditions of this License, they do not
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excuse you from the conditions of this License. If you cannot
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distribute so as to satisfy simultaneously your obligations under this
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License and any other pertinent obligations, then as a consequence you
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may not distribute the Program at all. For example, if a patent
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license would not permit royalty-free redistribution of the Program by
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all those who receive copies directly or indirectly through you, then
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the only way you could satisfy both it and this License would be to
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refrain entirely from distribution of the Program.
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If any portion of this section is held invalid or unenforceable under
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any particular circumstance, the balance of the section is intended to
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apply and the section as a whole is intended to apply in other
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circumstances.
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It is not the purpose of this section to induce you to infringe any
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patents or other property right claims or to contest validity of any
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such claims; this section has the sole purpose of protecting the
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integrity of the free software distribution system, which is
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implemented by public license practices. Many people have made
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generous contributions to the wide range of software distributed
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through that system in reliance on consistent application of that
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system; it is up to the author/donor to decide if he or she is willing
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to distribute software through any other system and a licensee cannot
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impose that choice.
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This section is intended to make thoroughly clear what is believed to
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be a consequence of the rest of this License.
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If the distribution and/or use of the Program is restricted in
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original copyright holder who places the Program under this License
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may add an explicit geographical distribution limitation excluding
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those countries, so that distribution is permitted only in or among
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countries not thus excluded. In such case, this License incorporates
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the limitation as if written in the body of this License.
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<LI>
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The Free Software Foundation may publish revised and/or new versions
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of the General Public License from time to time. Such new versions will
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be similar in spirit to the present version, but may differ in detail to
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address new problems or concerns.
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Each version is given a distinguishing version number. If the Program
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later version", you have the option of following the terms and conditions
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either of that version or of any later version published by the Free
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Software Foundation. If the Program does not specify a version number of
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this License, you may choose any version ever published by the Free Software
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Foundation.
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<LI>
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If you wish to incorporate parts of the Program into other free
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programs whose distribution conditions are different, write to the author
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to ask for permission. For software which is copyrighted by the Free
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Software Foundation, write to the Free Software Foundation; we sometimes
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make exceptions for this. Our decision will be guided by the two goals
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of preserving the free status of all derivatives of our free software and
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of promoting the sharing and reuse of software generally.
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NO WARRANTY
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<LI>
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BECAUSE THE PROGRAM IS LICENSED FREE OF CHARGE, THERE IS NO WARRANTY
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FOR THE PROGRAM, TO THE EXTENT PERMITTED BY APPLICABLE LAW. EXCEPT WHEN
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OTHERWISE STATED IN WRITING THE COPYRIGHT HOLDERS AND/OR OTHER PARTIES
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PROVIDE THE PROGRAM "AS IS" WITHOUT WARRANTY OF ANY KIND, EITHER EXPRESSED
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OR IMPLIED, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES OF
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MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE. THE ENTIRE RISK AS
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TO THE QUALITY AND PERFORMANCE OF THE PROGRAM IS WITH YOU. SHOULD THE
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PROGRAM PROVE DEFECTIVE, YOU ASSUME THE COST OF ALL NECESSARY SERVICING,
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REPAIR OR CORRECTION.
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<LI>
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IN NO EVENT UNLESS REQUIRED BY APPLICABLE LAW OR AGREED TO IN WRITING
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WILL ANY COPYRIGHT HOLDER, OR ANY OTHER PARTY WHO MAY MODIFY AND/OR
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REDISTRIBUTE THE PROGRAM AS PERMITTED ABOVE, BE LIABLE TO YOU FOR DAMAGES,
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INCLUDING ANY GENERAL, SPECIAL, INCIDENTAL OR CONSEQUENTIAL DAMAGES ARISING
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OUT OF THE USE OR INABILITY TO USE THE PROGRAM (INCLUDING BUT NOT LIMITED
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TO LOSS OF DATA OR DATA BEING RENDERED INACCURATE OR LOSSES SUSTAINED BY
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YOU OR THIRD PARTIES OR A FAILURE OF THE PROGRAM TO OPERATE WITH ANY OTHER
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PROGRAMS), EVEN IF SUCH HOLDER OR OTHER PARTY HAS BEEN ADVISED OF THE
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POSSIBILITY OF SUCH DAMAGES.
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</OL>
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<P>
|
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END OF TERMS AND CONDITIONS
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</P>
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|
|
|
|
|
<H2><A NAME="SEC3" HREF="gperf.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.
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|
|
|
</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.
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|
|
|
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>
|
|
|
|
|
|
<H1><A NAME="SEC4" HREF="gperf.html#TOC4">Contributors to GNU <CODE>gperf</CODE> Utility</A></H1>
|
|
|
|
|
|
<UL>
|
|
<LI>
|
|
|
|
<A NAME="IDX1"></A>
|
|
The GNU <CODE>gperf</CODE> perfect hash function generator utility was
|
|
written in GNU C++ by Douglas C. Schmidt. 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><bug-gnu-gperf@gnu.org></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>.
|
|
|
|
<LI>
|
|
|
|
Bruno Haible enhanced and optimized the search algorithm. He also rewrote
|
|
the input routines and the output routines for better reliability, and
|
|
added a testsuite.
|
|
</UL>
|
|
|
|
|
|
|
|
<H1><A NAME="SEC5" HREF="gperf.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> >= <VAR>n-1</VAR>. If <VAR>k</VAR>
|
|
= <VAR>n-1</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>
|
|
<CODE>gperf</CODE> currently generates the reserved keyword recognizer for
|
|
lexical analyzers in several production and research compilers and
|
|
language processing tools, including GNU C, GNU C++, GNU Java, GNU Pascal,
|
|
GNU Modula 3, and GNU indent. Complete C++ source code for <CODE>gperf</CODE> is
|
|
available from <CODE>http://ftp.gnu.org/pub/gnu/gperf/</CODE>.
|
|
A paper describing <CODE>gperf</CODE>'s design and implementation in greater
|
|
detail is available in the Second USENIX C++ Conference proceedings
|
|
or from <CODE>http://www.cs.wustl.edu/~schmidt/resume.html</CODE>.
|
|
|
|
</P>
|
|
|
|
|
|
<H1><A NAME="SEC6" HREF="gperf.html#TOC6">2 Static search structures and GNU <CODE>gperf</CODE></A></H1>
|
|
<P>
|
|
<A NAME="IDX2"></A>
|
|
|
|
</P>
|
|
<P>
|
|
A <EM>static search structure</EM> is an Abstract Data Type with certain
|
|
fundamental operations, e.g., <EM>initialize</EM>, <EM>insert</EM>,
|
|
and <EM>retrieve</EM>. Conceptually, all insertions occur before any
|
|
retrievals. In practice, <CODE>gperf</CODE> generates a <EM>static</EM> array
|
|
containing search set keywords and any associated attributes specified
|
|
by the user. Thus, there is essentially no execution-time cost for the
|
|
insertions. It is a useful data structure for representing <EM>static
|
|
search sets</EM>. Static search sets occur frequently in software system
|
|
applications. Typical static search sets include compiler reserved
|
|
words, assembler instruction opcodes, and built-in shell interpreter
|
|
commands. Search set members, called <EM>keywords</EM>, 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 Java, 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>
|
|
|
|
|
|
<H1><A NAME="SEC7" HREF="gperf.html#TOC7">3 High-Level Description of GNU <CODE>gperf</CODE></A></H1>
|
|
|
|
<P>
|
|
The perfect hash function generator <CODE>gperf</CODE> reads a set of
|
|
"keywords" from an input file (or from the standard input by
|
|
default). It attempts to derive a perfect hashing function that
|
|
recognizes a member of the <EM>static keyword set</EM> with at most a
|
|
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 bytes 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="SEC8" HREF="gperf.html#TOC8">3.1 Input Format to <CODE>gperf</CODE></A></H2>
|
|
<P>
|
|
<A NAME="IDX4"></A>
|
|
<A NAME="IDX5"></A>
|
|
<A NAME="IDX6"></A>
|
|
<A NAME="IDX7"></A>
|
|
You can control the input file 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>, the declarations section and
|
|
the functions section are optional. The following sections describe the
|
|
input format for each section.
|
|
|
|
</P>
|
|
|
|
<P>
|
|
It is possible to omit the declaration section entirely, if the <SAMP>`-t'</SAMP>
|
|
option is not given. In this case the input file begins directly with the
|
|
first keyword line, e.g.:
|
|
|
|
</P>
|
|
|
|
<PRE>
|
|
january
|
|
february
|
|
march
|
|
april
|
|
...
|
|
</PRE>
|
|
|
|
|
|
|
|
<H3><A NAME="SEC9" HREF="gperf.html#TOC9">3.1.1 Declarations</A></H3>
|
|
|
|
<P>
|
|
The keyword input file optionally contains a section for including
|
|
arbitrary C declarations and definitions, <CODE>gperf</CODE> declarations that
|
|
act like command-line options, as well as for providing a user-supplied
|
|
<CODE>struct</CODE>.
|
|
|
|
</P>
|
|
|
|
|
|
|
|
<H4><A NAME="SEC10" HREF="gperf.html#TOC10">3.1.1.1 User-supplied <CODE>struct</CODE></A></H4>
|
|
|
|
<P>
|
|
If the <SAMP>`-t'</SAMP> option (or, equivalently, the <SAMP>`%struct-type'</SAMP> declaration)
|
|
<EM>is</EM> enabled, you <EM>must</EM> provide a C <CODE>struct</CODE> as the last
|
|
component in the declaration section from the input file. The first
|
|
field in this struct must be of type <CODE>char *</CODE> or <CODE>const char *</CODE>
|
|
if the <SAMP>`-P'</SAMP> option is not given, or of type <CODE>int</CODE> if the option
|
|
<SAMP>`-P'</SAMP> (or, equivalently, the <SAMP>`%pic'</SAMP> declaration) is enabled.
|
|
This first field must be called <SAMP>`name'</SAMP>, although it is possible to modify
|
|
its name with the <SAMP>`-K'</SAMP> option (or, equivalently, the
|
|
<SAMP>`%define slot-name'</SAMP> declaration) described below.
|
|
|
|
</P>
|
|
<P>
|
|
Here is a simple example, using months of the year and their attributes as
|
|
input:
|
|
|
|
</P>
|
|
|
|
<PRE>
|
|
struct month { 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>
|
|
If the <CODE>struct</CODE> has already been declared in an include file, it can
|
|
be mentioned in an abbreviated form, like this:
|
|
|
|
</P>
|
|
|
|
<PRE>
|
|
struct month;
|
|
%%
|
|
january, 1, 31, 31
|
|
...
|
|
</PRE>
|
|
|
|
|
|
|
|
<H4><A NAME="SEC11" HREF="gperf.html#TOC11">3.1.1.2 Gperf Declarations</A></H4>
|
|
|
|
<P>
|
|
The declaration section can contain <CODE>gperf</CODE> declarations. They
|
|
influence the way <CODE>gperf</CODE> works, like command line options do.
|
|
In fact, every such declaration is equivalent to a command line option.
|
|
There are three forms of declarations:
|
|
|
|
</P>
|
|
|
|
<OL>
|
|
<LI>
|
|
|
|
Declarations without argument, like <SAMP>`%compare-lengths'</SAMP>.
|
|
|
|
<LI>
|
|
|
|
Declarations with an argument, like <SAMP>`%switch=<VAR>count</VAR>'</SAMP>.
|
|
|
|
<LI>
|
|
|
|
Declarations of names of entities in the output file, like
|
|
<SAMP>`%define lookup-function-name <VAR>name</VAR>'</SAMP>.
|
|
</OL>
|
|
|
|
<P>
|
|
When a declaration is given both in the input file and as a command line
|
|
option, the command-line option's value prevails.
|
|
|
|
</P>
|
|
<P>
|
|
The following <CODE>gperf</CODE> declarations are available.
|
|
|
|
</P>
|
|
<DL COMPACT>
|
|
|
|
<DT><SAMP>`%delimiters=<VAR>delimiter-list</VAR>'</SAMP>
|
|
<DD>
|
|
<A NAME="IDX9"></A>
|
|
Allows you to provide a string containing delimiters used to
|
|
separate keywords from their attributes. The default is ",". This
|
|
option is essential if you want to use keywords that have embedded
|
|
commas or newlines.
|
|
|
|
<DT><SAMP>`%struct-type'</SAMP>
|
|
<DD>
|
|
<A NAME="IDX10"></A>
|
|
Allows you to include a <CODE>struct</CODE> type declaration for generated
|
|
code; see above for an example.
|
|
|
|
<DT><SAMP>`%ignore-case'</SAMP>
|
|
<DD>
|
|
<A NAME="IDX11"></A>
|
|
Consider upper and lower case ASCII characters as equivalent. The string
|
|
comparison will use a case insignificant character comparison. Note that
|
|
locale dependent case mappings are ignored.
|
|
|
|
<DT><SAMP>`%language=<VAR>language-name</VAR>'</SAMP>
|
|
<DD>
|
|
<A NAME="IDX12"></A>
|
|
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&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>`%define slot-name <VAR>name</VAR>'</SAMP>
|
|
<DD>
|
|
<A NAME="IDX13"></A>
|
|
This declaration is only useful when option <SAMP>`-t'</SAMP> (or, equivalently, the
|
|
<SAMP>`%struct-type'</SAMP> declaration) 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>`%define initializer-suffix <VAR>initializers</VAR>'</SAMP>
|
|
<DD>
|
|
<A NAME="IDX14"></A>
|
|
This declaration is only useful when option <SAMP>`-t'</SAMP> (or, equivalently, the
|
|
<SAMP>`%struct-type'</SAMP> declaration) has been given.
|
|
It permits to specify initializers for the structure members following
|
|
<VAR>slot-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>slot-name</VAR>.
|
|
|
|
<DT><SAMP>`%define hash-function-name <VAR>name</VAR>'</SAMP>
|
|
<DD>
|
|
<A NAME="IDX15"></A>
|
|
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>`%define lookup-function-name <VAR>name</VAR>'</SAMP>
|
|
<DD>
|
|
<A NAME="IDX16"></A>
|
|
Allows you to specify the name for the generated lookup function.
|
|
Default name is <SAMP>`in_word_set'</SAMP>. This option permits multiple
|
|
generated hash functions to be used in the same application.
|
|
|
|
<DT><SAMP>`%define class-name <VAR>name</VAR>'</SAMP>
|
|
<DD>
|
|
<A NAME="IDX17"></A>
|
|
This option is only useful when option <SAMP>`-L C++'</SAMP> (or, equivalently,
|
|
the <SAMP>`%language=C++'</SAMP> declaration) has been given. It
|
|
allows you to specify the name of generated C++ class. Default name is
|
|
<CODE>Perfect_Hash</CODE>.
|
|
|
|
<DT><SAMP>`%7bit'</SAMP>
|
|
<DD>
|
|
<A NAME="IDX18"></A>
|
|
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 (bytes 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 byte is in this range. Only an explicit
|
|
test like <SAMP>`c >= 'A' && c <= 'Z''</SAMP> guarantees this.)
|
|
|
|
<DT><SAMP>`%compare-lengths'</SAMP>
|
|
<DD>
|
|
<A NAME="IDX19"></A>
|
|
Compare keyword lengths before trying a string comparison. This option
|
|
is mandatory for binary comparisons (see section <A HREF="gperf.html#SEC17">3.3 Use of NUL bytes</A>). It also might
|
|
cut down on the number of string comparisons made during the lookup, since
|
|
keywords with different lengths are never compared via <CODE>strcmp</CODE>.
|
|
However, using <SAMP>`%compare-lengths'</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> or <SAMP>`%switch'</SAMP> is not enabled), since the length
|
|
table contains as many elements as there are entries in the lookup table.
|
|
|
|
<DT><SAMP>`%compare-strncmp'</SAMP>
|
|
<DD>
|
|
<A NAME="IDX20"></A>
|
|
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>`%readonly-tables'</SAMP>
|
|
<DD>
|
|
<A NAME="IDX21"></A>
|
|
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>`%enum'</SAMP>
|
|
<DD>
|
|
<A NAME="IDX22"></A>
|
|
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><jjc@ai.mit.edu></CODE>.
|
|
|
|
<DT><SAMP>`%includes'</SAMP>
|
|
<DD>
|
|
<A NAME="IDX23"></A>
|
|
Include the necessary system include file, <CODE><string.h></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>`%global-table'</SAMP>
|
|
<DD>
|
|
<A NAME="IDX24"></A>
|
|
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>`%pic'</SAMP>
|
|
<DD>
|
|
<A NAME="IDX25"></A>
|
|
Optimize the generated table for inclusion in shared libraries. This
|
|
reduces the startup time of programs using a shared library containing
|
|
the generated code. If the <SAMP>`%struct-type'</SAMP> declaration (or,
|
|
equivalently, the option <SAMP>`-t'</SAMP>) is also given, the first field of the
|
|
user-defined struct must be of type <SAMP>`int'</SAMP>, not <SAMP>`char *'</SAMP>, because
|
|
it will contain offsets into the string pool instead of actual strings.
|
|
To convert such an offset to a string, you can use the expression
|
|
<SAMP>`stringpool + <VAR>o</VAR>'</SAMP>, where <VAR>o</VAR> is the offset. The string pool
|
|
name can be changed through the <SAMP>`%define string-pool-name'</SAMP> declaration.
|
|
|
|
<DT><SAMP>`%define string-pool-name <VAR>name</VAR>'</SAMP>
|
|
<DD>
|
|
<A NAME="IDX26"></A>
|
|
Allows you to specify the name of the generated string pool created by
|
|
the declaration <SAMP>`%pic'</SAMP> (or, equivalently, the option <SAMP>`-P'</SAMP>).
|
|
The default name is <SAMP>`stringpool'</SAMP>. This declaration permits the use of
|
|
two hash tables in the same file, with <SAMP>`%pic'</SAMP> and even when the
|
|
<SAMP>`%global-table'</SAMP> declaration (or, equivalently, the option <SAMP>`-G'</SAMP>)
|
|
is given.
|
|
|
|
<DT><SAMP>`%null-strings'</SAMP>
|
|
<DD>
|
|
<A NAME="IDX27"></A>
|
|
Use NULL strings instead of empty strings for empty keyword table entries.
|
|
This reduces the startup time of programs using a shared library containing
|
|
the generated code (but not as much as the declaration <SAMP>`%pic'</SAMP>), at the
|
|
expense of one more test-and-branch instruction at run time.
|
|
|
|
<DT><SAMP>`%define word-array-name <VAR>name</VAR>'</SAMP>
|
|
<DD>
|
|
<A NAME="IDX28"></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>
|
|
(or, equivalently, the <SAMP>`%global-table'</SAMP> declaration) is given.
|
|
|
|
<DT><SAMP>`%define length-table-name <VAR>name</VAR>'</SAMP>
|
|
<DD>
|
|
<A NAME="IDX29"></A>
|
|
Allows you to specify the name for the generated array containing the
|
|
length table. Default name is <SAMP>`lengthtable'</SAMP>. This option permits the
|
|
use of two length tables in the same file, even when the option <SAMP>`-G'</SAMP>
|
|
(or, equivalently, the <SAMP>`%global-table'</SAMP> declaration) is given.
|
|
|
|
<DT><SAMP>`%switch=<VAR>count</VAR>'</SAMP>
|
|
<DD>
|
|
<A NAME="IDX30"></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 input files. 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>`%omit-struct-type'</SAMP>
|
|
<DD>
|
|
<A NAME="IDX31"></A>
|
|
Prevents the transfer of the type declaration to the output file. Use
|
|
this option if the type is already defined elsewhere.
|
|
</DL>
|
|
|
|
|
|
|
|
<H4><A NAME="SEC12" HREF="gperf.html#TOC12">3.1.1.3 C Code Inclusion</A></H4>
|
|
|
|
<P>
|
|
<A NAME="IDX32"></A>
|
|
<A NAME="IDX33"></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 <assert.h>
|
|
/* This section of code is inserted directly into the output. */
|
|
int return_month_days (struct month *months, int is_leap_year);
|
|
%}
|
|
struct month { char *name; int number; int days; int leap_days; };
|
|
%%
|
|
january, 1, 31, 31
|
|
february, 2, 28, 29
|
|
march, 3, 31, 31
|
|
...
|
|
</PRE>
|
|
|
|
|
|
|
|
<H3><A NAME="SEC13" HREF="gperf.html#TOC13">3.1.2 Format for Keyword Entries</A></H3>
|
|
|
|
<P>
|
|
The second input file 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. A line
|
|
beginning with <SAMP>`%'</SAMP> in the first column is an option declaration and
|
|
must not occur within the keywords section.
|
|
|
|
</P>
|
|
<P>
|
|
The first field of each non-comment line is always the keyword 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 (or, equivalently, the
|
|
<SAMP>`%struct-type'</SAMP> declaration) is <EM>not</EM> enabled
|
|
these fields are simply ignored. All previous examples except the last
|
|
one contain keyword attributes.
|
|
|
|
</P>
|
|
|
|
|
|
<H3><A NAME="SEC14" HREF="gperf.html#TOC14">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>
|
|
|
|
|
|
<H3><A NAME="SEC15" HREF="gperf.html#TOC15">3.1.4 Where to place directives for GNU <CODE>indent</CODE>.</A></H3>
|
|
|
|
<P>
|
|
If you want to invoke GNU <CODE>indent</CODE> on a <CODE>gperf</CODE> input file,
|
|
you will see that GNU <CODE>indent</CODE> doesn't understand the <SAMP>`%%'</SAMP>,
|
|
<SAMP>`%{'</SAMP> and <SAMP>`%}'</SAMP> directives that control <CODE>gperf</CODE>'s
|
|
interpretation of the input file. Therefore you have to insert some
|
|
directives for GNU <CODE>indent</CODE>. More precisely, assuming the most
|
|
general input file structure
|
|
|
|
</P>
|
|
|
|
<PRE>
|
|
declarations part 1
|
|
%{
|
|
verbatim code
|
|
%}
|
|
declarations part 2
|
|
%%
|
|
keywords
|
|
%%
|
|
functions
|
|
</PRE>
|
|
|
|
<P>
|
|
you would insert <SAMP>`*INDENT-OFF*'</SAMP> and <SAMP>`*INDENT-ON*'</SAMP> comments
|
|
as follows:
|
|
|
|
</P>
|
|
|
|
<PRE>
|
|
/* *INDENT-OFF* */
|
|
declarations part 1
|
|
%{
|
|
/* *INDENT-ON* */
|
|
verbatim code
|
|
/* *INDENT-OFF* */
|
|
%}
|
|
declarations part 2
|
|
%%
|
|
keywords
|
|
%%
|
|
/* *INDENT-ON* */
|
|
functions
|
|
</PRE>
|
|
|
|
|
|
|
|
<H2><A NAME="SEC16" HREF="gperf.html#TOC16">3.2 Output Format for Generated C Code with <CODE>gperf</CODE></A></H2>
|
|
<P>
|
|
<A NAME="IDX34"></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="IDX35"></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> byte
|
|
positions indexed into an <EM>associated values</EM> 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>. The relevant selected positions (i.e. indices
|
|
into <VAR>str</VAR>) 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.html#SEC18">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="IDX36"></A>
|
|
If <VAR>str</VAR> is in the keyword set, returns a pointer to that
|
|
keyword. More exactly, if the option <SAMP>`-t'</SAMP> (or, equivalently, the
|
|
<SAMP>`%struct-type'</SAMP> declaration) 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> (or, equivalently, the <SAMP>`%compare-strncmp'</SAMP>
|
|
declaration) is not used, <VAR>str</VAR> must be a NUL terminated
|
|
string of exactly length <VAR>len</VAR>. If <SAMP>`-c'</SAMP> (or, equivalently, the
|
|
<SAMP>`%compare-strncmp'</SAMP> declaration) is used, <VAR>str</VAR> must
|
|
simply be an array of <VAR>len</VAR> bytes 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="IDX37"></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 (or, equivalently, the
|
|
<SAMP>`%struct-type'</SAMP> and <SAMP>`%switch'</SAMP> declarations) are omitted, the default
|
|
action
|
|
is to generate a <CODE>char *</CODE> array containing the keywords, together with
|
|
additional empty 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="SEC17" HREF="gperf.html#TOC17">3.3 Use of NUL bytes</A></H2>
|
|
<P>
|
|
<A NAME="IDX38"></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 bytes,
|
|
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> (or, equivalently, the <SAMP>`%compare-strncmp'</SAMP>
|
|
declaration) 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
|
|
bytes.
|
|
|
|
</P>
|
|
<P>
|
|
If option <SAMP>`-l'</SAMP> (or, equivalently, the <SAMP>`%compare-lengths'</SAMP>
|
|
declaration) is used, then the hash table performs binary
|
|
comparison. The keywords in the input file may contain NUL bytes,
|
|
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 byte.
|
|
Also, in this case the <SAMP>`-c'</SAMP> option (or, equivalently, the
|
|
<SAMP>`%compare-strncmp'</SAMP> declaration) is ignored.
|
|
|
|
</P>
|
|
|
|
|
|
<H1><A NAME="SEC18" HREF="gperf.html#TOC18">4 Invoking <CODE>gperf</CODE></A></H1>
|
|
|
|
<P>
|
|
There are <EM>many</EM> options to <CODE>gperf</CODE>. They were added to make
|
|
the program more convenient for use with real applications. "On-line"
|
|
help is readily available via the <SAMP>`--help'</SAMP> option. Here is the
|
|
complete list of options.
|
|
|
|
</P>
|
|
|
|
|
|
|
|
<H2><A NAME="SEC19" HREF="gperf.html#TOC19">4.1 Specifying the Location of the Output File</A></H2>
|
|
|
|
<DL COMPACT>
|
|
|
|
<DT><SAMP>`--output-file=<VAR>file</VAR>'</SAMP>
|
|
<DD>
|
|
Allows you to specify the name of the file to which the output is written to.
|
|
</DL>
|
|
|
|
<P>
|
|
The results are written to standard output if no output file is specified
|
|
or if it is <SAMP>`-'</SAMP>.
|
|
|
|
</P>
|
|
|
|
|
|
<H2><A NAME="SEC20" HREF="gperf.html#TOC20">4.2 Options that affect Interpretation of the Input File</A></H2>
|
|
|
|
<P>
|
|
These options are also available as declarations in the input file
|
|
(see section <A HREF="gperf.html#SEC11">3.1.1.2 Gperf Declarations</A>).
|
|
|
|
</P>
|
|
<DL COMPACT>
|
|
|
|
<DT><SAMP>`-e <VAR>keyword-delimiter-list</VAR>'</SAMP>
|
|
<DD>
|
|
<DT><SAMP>`--delimiters=<VAR>keyword-delimiter-list</VAR>'</SAMP>
|
|
<DD>
|
|
<A NAME="IDX39"></A>
|
|
Allows you to provide a string containing delimiters used to
|
|
separate keywords from their attributes. The default is ",". 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>
|
|
<DT><SAMP>`--struct-type'</SAMP>
|
|
<DD>
|
|
Allows you to include a <CODE>struct</CODE> type declaration for generated
|
|
code. Any text before a pair of consecutive <SAMP>`%%'</SAMP> is considered
|
|
part of the type declaration. Keywords 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, C++, Pascal, Modula 2,
|
|
Modula 3 and JavaScript reserved words are distributed with this release.
|
|
|
|
<DT><SAMP>`--ignore-case'</SAMP>
|
|
<DD>
|
|
Consider upper and lower case ASCII characters as equivalent. The string
|
|
comparison will use a case insignificant character comparison. Note that
|
|
locale dependent case mappings are ignored. This option is therefore not
|
|
suitable if a properly internationalized or locale aware case mapping
|
|
should be used. (For example, in a Turkish locale, the upper case equivalent
|
|
of the lowercase ASCII letter <SAMP>`i'</SAMP> is the non-ASCII character
|
|
<SAMP>`capital i with dot above'</SAMP>.) For this case, it is better to apply
|
|
an uppercase or lowercase conversion on the string before passing it to
|
|
the <CODE>gperf</CODE> generated function.
|
|
</DL>
|
|
|
|
|
|
|
|
<H2><A NAME="SEC21" HREF="gperf.html#TOC21">4.3 Options to specify the Language for the Output Code</A></H2>
|
|
|
|
<P>
|
|
These options are also available as declarations in the input file
|
|
(see section <A HREF="gperf.html#SEC11">3.1.1.2 Gperf Declarations</A>).
|
|
|
|
</P>
|
|
<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&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="SEC22" HREF="gperf.html#TOC22">4.4 Options for fine tuning Details in the Output Code</A></H2>
|
|
|
|
<P>
|
|
Most of these options are also available as declarations in the input file
|
|
(see section <A HREF="gperf.html#SEC11">3.1.1.2 Gperf Declarations</A>).
|
|
|
|
</P>
|
|
<DL COMPACT>
|
|
|
|
<DT><SAMP>`-K <VAR>slot-name</VAR>'</SAMP>
|
|
<DD>
|
|
<DT><SAMP>`--slot-name=<VAR>slot-name</VAR>'</SAMP>
|
|
<DD>
|
|
<A NAME="IDX40"></A>
|
|
This option is only useful when option <SAMP>`-t'</SAMP> (or, equivalently, the
|
|
<SAMP>`%struct-type'</SAMP> declaration) 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="IDX41"></A>
|
|
This option is only useful when option <SAMP>`-t'</SAMP> (or, equivalently, the
|
|
<SAMP>`%struct-type'</SAMP> declaration) has been given.
|
|
It permits to specify initializers for the structure members following
|
|
<VAR>slot-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>slot-name</VAR>.
|
|
|
|
<DT><SAMP>`-H <VAR>hash-function-name</VAR>'</SAMP>
|
|
<DD>
|
|
<DT><SAMP>`--hash-function-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-function-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 multiple
|
|
generated hash functions to be 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="IDX42"></A>
|
|
This option is only useful when option <SAMP>`-L C++'</SAMP> (or, equivalently,
|
|
the <SAMP>`%language=C++'</SAMP> declaration) 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 (bytes 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 byte is in this range. Only an explicit
|
|
test like <SAMP>`c >= 'A' && c <= 'Z''</SAMP> guarantees this.) This was the
|
|
default in versions of <CODE>gperf</CODE> earlier than 2.7; now the default is
|
|
to support 8-bit and multibyte characters.
|
|
|
|
<DT><SAMP>`-l'</SAMP>
|
|
<DD>
|
|
<DT><SAMP>`--compare-lengths'</SAMP>
|
|
<DD>
|
|
Compare keyword lengths before trying a string comparison. This option
|
|
is mandatory for binary comparisons (see section <A HREF="gperf.html#SEC17">3.3 Use of NUL bytes</A>). It also might
|
|
cut down on the number of string comparisons made during the lookup, since
|
|
keywords 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> or <SAMP>`%switch'</SAMP> is not enabled), since the length
|
|
table contains as many elements as there are entries in the lookup table.
|
|
|
|
<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><jjc@ai.mit.edu></CODE>.
|
|
|
|
<DT><SAMP>`-I'</SAMP>
|
|
<DD>
|
|
<DT><SAMP>`--includes'</SAMP>
|
|
<DD>
|
|
Include the necessary system include file, <CODE><string.h></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-table'</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>`-P'</SAMP>
|
|
<DD>
|
|
<DT><SAMP>`--pic'</SAMP>
|
|
<DD>
|
|
Optimize the generated table for inclusion in shared libraries. This
|
|
reduces the startup time of programs using a shared library containing
|
|
the generated code. If the option <SAMP>`-t'</SAMP> (or, equivalently, the
|
|
<SAMP>`%struct-type'</SAMP> declaration) is also given, the first field of the
|
|
user-defined struct must be of type <SAMP>`int'</SAMP>, not <SAMP>`char *'</SAMP>, because
|
|
it will contain offsets into the string pool instead of actual strings.
|
|
To convert such an offset to a string, you can use the expression
|
|
<SAMP>`stringpool + <VAR>o</VAR>'</SAMP>, where <VAR>o</VAR> is the offset. The string pool
|
|
name can be changed through the option <SAMP>`--string-pool-name'</SAMP>.
|
|
|
|
<DT><SAMP>`-Q <VAR>string-pool-name</VAR>'</SAMP>
|
|
<DD>
|
|
<DT><SAMP>`--string-pool-name=<VAR>string-pool-name</VAR>'</SAMP>
|
|
<DD>
|
|
Allows you to specify the name of the generated string pool created by
|
|
option <SAMP>`-P'</SAMP>. The default name is <SAMP>`stringpool'</SAMP>. This option
|
|
permits the use of two hash tables in the same file, with <SAMP>`-P'</SAMP> and
|
|
even when the option <SAMP>`-G'</SAMP> (or, equivalently, the <SAMP>`%global-table'</SAMP>
|
|
declaration) is given.
|
|
|
|
<DT><SAMP>`--null-strings'</SAMP>
|
|
<DD>
|
|
Use NULL strings instead of empty strings for empty keyword table entries.
|
|
This reduces the startup time of programs using a shared library containing
|
|
the generated code (but not as much as option <SAMP>`-P'</SAMP>), at the expense
|
|
of one more test-and-branch instruction at run time.
|
|
|
|
<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="IDX43"></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>
|
|
(or, equivalently, the <SAMP>`%global-table'</SAMP> declaration) is given.
|
|
|
|
<DT><SAMP>`--length-table-name=<VAR>length-table-array-name</VAR>'</SAMP>
|
|
<DD>
|
|
<A NAME="IDX44"></A>
|
|
Allows you to specify the name for the generated array containing the
|
|
length table. Default name is <SAMP>`lengthtable'</SAMP>. This option permits the
|
|
use of two length tables in the same file, even when the option <SAMP>`-G'</SAMP>
|
|
(or, equivalently, the <SAMP>`%global-table'</SAMP> declaration) is given.
|
|
|
|
<DT><SAMP>`-S <VAR>total-switch-statements</VAR>'</SAMP>
|
|
<DD>
|
|
<DT><SAMP>`--switch=<VAR>total-switch-statements</VAR>'</SAMP>
|
|
<DD>
|
|
<A NAME="IDX45"></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 input files. 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="SEC23" HREF="gperf.html#TOC23">4.5 Options for changing the Algorithms employed by <CODE>gperf</CODE></A></H2>
|
|
|
|
<DL COMPACT>
|
|
|
|
<DT><SAMP>`-k <VAR>selected-byte-positions</VAR>'</SAMP>
|
|
<DD>
|
|
<DT><SAMP>`--key-positions=<VAR>selected-byte-positions</VAR>'</SAMP>
|
|
<DD>
|
|
Allows selection of the byte positions used in the keywords'
|
|
hash function. The allowable choices range between 1-255, 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 wildcard '*' causes the generated
|
|
hash function to consider <STRONG>all</STRONG> byte positions in each keyword,
|
|
whereas '$' instructs the hash function to use the "final byte"
|
|
of a keyword (this is the only way to use a byte position greater than
|
|
255, incidentally).
|
|
|
|
For instance, the option <SAMP>`-k 1,2,4,6-10,'$''</SAMP> generates a hash
|
|
function that considers positions 1,2,4,6,7,8,9,10, plus the last
|
|
byte in each keyword (which may be at a different position for each
|
|
keyword, obviously). Keywords
|
|
with length less than the indicated byte positions work properly, since
|
|
selected byte positions exceeding the keyword length are simply not
|
|
referenced in the hash function.
|
|
|
|
This option is not normally needed since version 2.8 of <CODE>gperf</CODE>;
|
|
the default byte positions are computed depending on the keyword set,
|
|
through a search that minimizes the number of byte positions.
|
|
|
|
<DT><SAMP>`-D'</SAMP>
|
|
<DD>
|
|
<DT><SAMP>`--duplicates'</SAMP>
|
|
<DD>
|
|
<A NAME="IDX46"></A>
|
|
Handle keywords whose selected byte sets hash to duplicate values.
|
|
Duplicate hash values can occur if a set of keywords has the same names, but
|
|
possesses different attributes, or if the selected byte positions are not well
|
|
chosen. With the -D option <CODE>gperf</CODE> treats all these keywords as
|
|
part of an equivalence class and generates a perfect hash function with
|
|
multiple comparisons for duplicate keywords. 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.
|
|
|
|
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>`-m <VAR>iterations</VAR>'</SAMP>
|
|
<DD>
|
|
<DT><SAMP>`--multiple-iterations=<VAR>iterations</VAR>'</SAMP>
|
|
<DD>
|
|
Perform multiple choices of the <SAMP>`-i'</SAMP> and <SAMP>`-j'</SAMP> values, and
|
|
choose the best results. This increases the running time by a factor of
|
|
<VAR>iterations</VAR> but does a good job minimizing the generated table size.
|
|
|
|
<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> (or, equivalently,
|
|
<SAMP>`%switch'</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="IDX47"></A>
|
|
Affects the "jump value", i.e., how far to advance the associated
|
|
byte 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>`-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.
|
|
|
|
<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 keywords.
|
|
It can be written as an integer, a floating-point number or a fraction.
|
|
For example, a value of 3 means "allow the maximum associated value to be
|
|
about 3 times larger than the number of input keywords".
|
|
Conversely, a value of 1/3 means "allow the maximum associated value to
|
|
be about 3 times smaller than the number of input keywords". Values
|
|
smaller than 1 are useful for limiting the overall size of the generated hash
|
|
table, though the option <SAMP>`-m'</SAMP> is better at this purpose.
|
|
|
|
If `generate switch' option <SAMP>`-S'</SAMP> (or, equivalently, <SAMP>`%switch'</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 keywords (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.
|
|
</DL>
|
|
|
|
|
|
|
|
<H2><A NAME="SEC24" HREF="gperf.html#TOC24">4.6 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>
|
|
|
|
|
|
|
|
<H1><A NAME="SEC25" HREF="gperf.html#TOC25">5 Known Bugs and Limitations with <CODE>gperf</CODE></A></H1>
|
|
|
|
<P>
|
|
The following are some limitations with the current release of
|
|
<CODE>gperf</CODE>:
|
|
|
|
</P>
|
|
|
|
<UL>
|
|
<LI>
|
|
|
|
The <CODE>gperf</CODE> utility is tuned to execute quickly, and works quickly
|
|
for small to medium size data sets (around 1000 keywords). It is
|
|
extremely useful for maintaining perfect hash functions for compiler
|
|
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.
|
|
|
|
<LI>
|
|
|
|
The size of the generate static keyword array can get <EM>extremely</EM>
|
|
large if the input keyword file is large or if the keywords are quite
|
|
similar. This tends to slow down the compilation of the generated C
|
|
code, and <EM>greatly</EM> inflates the object code size. If this
|
|
situation occurs, consider using the <SAMP>`-S'</SAMP> option to reduce data
|
|
size, potentially increasing keyword recognition time a negligible
|
|
amount. Since many C compilers cannot correctly generate 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.
|
|
|
|
<LI>
|
|
|
|
The maximum number of selected byte positions has an
|
|
arbitrary limit of 255. This restriction should be removed, and if
|
|
anyone considers this a problem write me and let me know so I can remove
|
|
the constraint.
|
|
</UL>
|
|
|
|
|
|
|
|
<H1><A NAME="SEC26" HREF="gperf.html#TOC26">6 Things Still Left to Do</A></H1>
|
|
|
|
<P>
|
|
It should be "relatively" easy to replace the current perfect hash
|
|
function algorithm with a more exhaustive approach; the perfect hash
|
|
module is essential independent from other program modules. Additional
|
|
worthwhile improvements include:
|
|
|
|
</P>
|
|
|
|
<UL>
|
|
<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).
|
|
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 an Ada package as the code output, in addition to the current
|
|
C and C++ routines.
|
|
</UL>
|
|
|
|
|
|
|
|
<H1><A NAME="SEC27" HREF="gperf.html#TOC27">7 Bibliography</A></H1>
|
|
|
|
<P>
|
|
[1] Chang, C.C.: <I>A Scheme for Constructing Ordered Minimal Perfect
|
|
Hashing Functions</I> Information Sciences 39(1986), 187-195.
|
|
|
|
</P>
|
|
<P>
|
|
[2] Cichelli, Richard J. <I>Author's Response to "On Cichelli's Minimal Perfect Hash
|
|
Functions Method"</I> Communications of the ACM, 23, 12(December 1980), 729.
|
|
|
|
</P>
|
|
<P>
|
|
[3] Cichelli, Richard J. <I>Minimal Perfect Hash Functions Made Simple</I>
|
|
Communications of the ACM, 23, 1(January 1980), 17-19.
|
|
|
|
</P>
|
|
<P>
|
|
[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>
|
|
[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.
|
|
|
|
</P>
|
|
<P>
|
|
[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] Schmidt, Douglas C. <I>GPERF: A Perfect Hash Function Generator</I>
|
|
C++ Report, SIGS 10 10 (November/December 1998).
|
|
|
|
</P>
|
|
<P>
|
|
[11] 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>
|
|
[12] 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>
|
|
[13] Stallman, Richard M. <I>Using and Porting GNU CC</I> Free Software Foundation,
|
|
1988.
|
|
|
|
</P>
|
|
<P>
|
|
[14] Stroustrup, Bjarne <I>The C++ Programming Language.</I> Addison-Wesley, 1986.
|
|
|
|
</P>
|
|
<P>
|
|
[15] Tiemann, Michael D. <I>User's Guide to GNU C++</I> Free Software
|
|
Foundation, 1989.
|
|
|
|
</P>
|
|
|
|
|
|
<H1><A NAME="SEC28" HREF="gperf.html#TOC28">Concept Index</A></H1>
|
|
|
|
<P>
|
|
Jump to:
|
|
<A HREF="#cindex_%">%</A>
|
|
-
|
|
<A HREF="#cindex_a">a</A>
|
|
-
|
|
<A HREF="#cindex_b">b</A>
|
|
-
|
|
<A HREF="#cindex_c">c</A>
|
|
-
|
|
<A HREF="#cindex_d">d</A>
|
|
-
|
|
<A HREF="#cindex_f">f</A>
|
|
-
|
|
<A HREF="#cindex_h">h</A>
|
|
-
|
|
<A HREF="#cindex_i">i</A>
|
|
-
|
|
<A HREF="#cindex_j">j</A>
|
|
-
|
|
<A HREF="#cindex_k">k</A>
|
|
-
|
|
<A HREF="#cindex_m">m</A>
|
|
-
|
|
<A HREF="#cindex_n">n</A>
|
|
-
|
|
<A HREF="#cindex_s">s</A>
|
|
<P>
|
|
<H2><A NAME="cindex_%">%</A></H2>
|
|
<DIR>
|
|
<LI><A HREF="gperf.html#IDX8"><SAMP>`%%'</SAMP></A>
|
|
<LI><A HREF="gperf.html#IDX18"><SAMP>`%7bit'</SAMP></A>
|
|
<LI><A HREF="gperf.html#IDX19"><SAMP>`%compare-lengths'</SAMP></A>
|
|
<LI><A HREF="gperf.html#IDX20"><SAMP>`%compare-strncmp'</SAMP></A>
|
|
<LI><A HREF="gperf.html#IDX17"><SAMP>`%define class-name'</SAMP></A>
|
|
<LI><A HREF="gperf.html#IDX15"><SAMP>`%define hash-function-name'</SAMP></A>
|
|
<LI><A HREF="gperf.html#IDX14"><SAMP>`%define initializer-suffix'</SAMP></A>
|
|
<LI><A HREF="gperf.html#IDX29"><SAMP>`%define length-table-name'</SAMP></A>
|
|
<LI><A HREF="gperf.html#IDX16"><SAMP>`%define lookup-function-name'</SAMP></A>
|
|
<LI><A HREF="gperf.html#IDX13"><SAMP>`%define slot-name'</SAMP></A>
|
|
<LI><A HREF="gperf.html#IDX26"><SAMP>`%define string-pool-name'</SAMP></A>
|
|
<LI><A HREF="gperf.html#IDX28"><SAMP>`%define word-array-name'</SAMP></A>
|
|
<LI><A HREF="gperf.html#IDX9"><SAMP>`%delimiters'</SAMP></A>
|
|
<LI><A HREF="gperf.html#IDX22"><SAMP>`%enum'</SAMP></A>
|
|
<LI><A HREF="gperf.html#IDX24"><SAMP>`%global-table'</SAMP></A>
|
|
<LI><A HREF="gperf.html#IDX11"><SAMP>`%ignore-case'</SAMP></A>
|
|
<LI><A HREF="gperf.html#IDX23"><SAMP>`%includes'</SAMP></A>
|
|
<LI><A HREF="gperf.html#IDX12"><SAMP>`%language'</SAMP></A>
|
|
<LI><A HREF="gperf.html#IDX27"><SAMP>`%null-strings'</SAMP></A>
|
|
<LI><A HREF="gperf.html#IDX31"><SAMP>`%omit-struct-type'</SAMP></A>
|
|
<LI><A HREF="gperf.html#IDX25"><SAMP>`%pic'</SAMP></A>
|
|
<LI><A HREF="gperf.html#IDX21"><SAMP>`%readonly-tables'</SAMP></A>
|
|
<LI><A HREF="gperf.html#IDX10"><SAMP>`%struct-type'</SAMP></A>
|
|
<LI><A HREF="gperf.html#IDX30"><SAMP>`%switch'</SAMP></A>
|
|
<LI><A HREF="gperf.html#IDX32"><SAMP>`%{'</SAMP></A>
|
|
<LI><A HREF="gperf.html#IDX33"><SAMP>`%}'</SAMP></A>
|
|
</DIR>
|
|
<H2><A NAME="cindex_a">a</A></H2>
|
|
<DIR>
|
|
<LI><A HREF="gperf.html#IDX43">Array name</A>, <A HREF="gperf.html#IDX44">Array name</A>
|
|
</DIR>
|
|
<H2><A NAME="cindex_b">b</A></H2>
|
|
<DIR>
|
|
<LI><A HREF="gperf.html#IDX1">Bugs</A>
|
|
</DIR>
|
|
<H2><A NAME="cindex_c">c</A></H2>
|
|
<DIR>
|
|
<LI><A HREF="gperf.html#IDX42">Class name</A>
|
|
</DIR>
|
|
<H2><A NAME="cindex_d">d</A></H2>
|
|
<DIR>
|
|
<LI><A HREF="gperf.html#IDX5">Declaration section</A>
|
|
<LI><A HREF="gperf.html#IDX39">Delimiters</A>
|
|
<LI><A HREF="gperf.html#IDX46">Duplicates</A>
|
|
</DIR>
|
|
<H2><A NAME="cindex_f">f</A></H2>
|
|
<DIR>
|
|
<LI><A HREF="gperf.html#IDX4">Format</A>
|
|
<LI><A HREF="gperf.html#IDX7">Functions section</A>
|
|
</DIR>
|
|
<H2><A NAME="cindex_h">h</A></H2>
|
|
<DIR>
|
|
<LI><A HREF="gperf.html#IDX35">hash</A>
|
|
<LI><A HREF="gperf.html#IDX34">hash table</A>
|
|
</DIR>
|
|
<H2><A NAME="cindex_i">i</A></H2>
|
|
<DIR>
|
|
<LI><A HREF="gperf.html#IDX36">in_word_set</A>
|
|
<LI><A HREF="gperf.html#IDX41">Initializers</A>
|
|
</DIR>
|
|
<H2><A NAME="cindex_j">j</A></H2>
|
|
<DIR>
|
|
<LI><A HREF="gperf.html#IDX47">Jump value</A>
|
|
</DIR>
|
|
<H2><A NAME="cindex_k">k</A></H2>
|
|
<DIR>
|
|
<LI><A HREF="gperf.html#IDX6">Keywords section</A>
|
|
</DIR>
|
|
<H2><A NAME="cindex_m">m</A></H2>
|
|
<DIR>
|
|
<LI><A HREF="gperf.html#IDX3">Minimal perfect hash functions</A>
|
|
</DIR>
|
|
<H2><A NAME="cindex_n">n</A></H2>
|
|
<DIR>
|
|
<LI><A HREF="gperf.html#IDX38">NUL</A>
|
|
</DIR>
|
|
<H2><A NAME="cindex_s">s</A></H2>
|
|
<DIR>
|
|
<LI><A HREF="gperf.html#IDX40">Slot name</A>
|
|
<LI><A HREF="gperf.html#IDX2">Static search structure</A>
|
|
<LI><A HREF="gperf.html#IDX37"><CODE>switch</CODE></A>, <A HREF="gperf.html#IDX45"><CODE>switch</CODE></A>
|
|
</DIR>
|
|
|
|
</P>
|
|
<P><HR><P>
|
|
This document was generated on 13 January 2006 using the
|
|
<A HREF="http://wwwinfo.cern.ch/dis/texi2html/">texi2html</A>
|
|
translator version 1.52.</P>
|
|
</BODY>
|
|
</HTML>
|