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<HTML>
<HEAD>
<!-- This HTML file has been created by texi2html 1.51
from gperf.texi on 15 April 1998 -->
<TITLE>User's Guide to gperf - 5 Known Bugs and Limitations with gperf</TITLE>
</HEAD>
<BODY>
Go to the <A HREF="gperf_1.html">first</A>, <A HREF="gperf_7.html">previous</A>, <A HREF="gperf_9.html">next</A>, <A HREF="gperf_11.html">last</A> section, <A HREF="gperf_toc.html">table of contents</A>.
<P><HR><P>
<H1><A NAME="SEC20" HREF="gperf_toc.html#TOC20">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.
However, since <CODE>gperf</CODE> does not backtrack no guaranteed solution
occurs on every run. On the other hand, it is usually easy to obtain a
solution by varying the option parameters. In particular, try the
<SAMP>`-r'</SAMP> option, and also try changing the default arguments to the
<SAMP>`-s'</SAMP> and <SAMP>`-j'</SAMP> options. To <EM>guarantee</EM> a solution, use
the <SAMP>`-D'</SAMP> and <SAMP>`-S'</SAMP> options, although the final results are not
likely to be a <EM>perfect</EM> hash function anymore! Finally, use the
<SAMP>`-f'</SAMP> option if you want <CODE>gperf</CODE> to generate the perfect hash
function <EM>fast</EM>, with less emphasis on making it minimal.
<LI>
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 generated code for
large switch statements it is important to qualify the <VAR>-S</VAR> option
with an appropriate numerical argument that controls the number of
switch statements generated.
<LI>
The maximum number of key positions selected for a given key has an
arbitrary limit of 126. 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>
<P><HR><P>
Go to the <A HREF="gperf_1.html">first</A>, <A HREF="gperf_7.html">previous</A>, <A HREF="gperf_9.html">next</A>, <A HREF="gperf_11.html">last</A> section, <A HREF="gperf_toc.html">table of contents</A>.
</BODY>
</HTML>