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Bruno Haible
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<HTML>
<HEAD>
<!-- This HTML file has been created by texi2html 1.51
from gperf.texi on 15 April 1998 -->
from gperf.texi on 20 August 2000 -->
<TITLE>User's Guide to gperf - 6 Things Still Left to Do</TITLE>
<TITLE>Perfect Hash Function Generator - 7 Implementation Details of GNU gperf</TITLE>
</HEAD>
<BODY>
Go to the <A HREF="gperf_1.html">first</A>, <A HREF="gperf_8.html">previous</A>, <A HREF="gperf_10.html">next</A>, <A HREF="gperf_11.html">last</A> section, <A HREF="gperf_toc.html">table of contents</A>.
<P><HR><P>
<H1><A NAME="SEC21" HREF="gperf_toc.html#TOC21">6 Things Still Left to Do</A></H1>
<H1><A NAME="SEC22" HREF="gperf_toc.html#TOC22">7 Implementation Details of GNU <CODE>gperf</CODE></A></H1>
<P>
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:
A paper describing the high-level description of the data structures and
algorithms used to implement <CODE>gperf</CODE> will soon be available. This
paper is useful not only from a maintenance and enhancement perspective,
but also because they demonstrate several clever and useful programming
techniques, e.g., `Iteration Number' boolean arrays, double
hashing, a "safe" and efficient method for reading arbitrarily long
input from a file, and a provably optimal algorithm for simultaneously
determining both the minimum and maximum elements in a list.
</P>
<UL>
<LI>
Make the algorithm more robust. At present, the program halts with an
error diagnostic if it can't find a direct solution and the <SAMP>`-D'</SAMP>
option is not enabled. A more comprehensive, albeit computationally
expensive, approach would employ backtracking or enable alternative
options and retry. It's not clear how helpful this would be, in
general, since most search sets are rather small in practice.
<LI>
Another useful extension involves modifying the program to generate
"minimal" perfect hash functions (under certain circumstances, the
current version can be rather extravagant in the generated table size).
Again, this is mostly of theoretical interest, since a sparse table
often produces faster lookups, and use of the <SAMP>`-S'</SAMP> <CODE>switch</CODE>
option can minimize the data size, at the expense of slightly longer
lookups (note that the gcc compiler generally produces good code for
<CODE>switch</CODE> statements, reducing the need for more complex schemes).
<LI>
In addition to improving the algorithm, it would also be useful to
generate a C++ class or Ada package as the code output, in addition to
the current C routines.
</UL>
<P><HR><P>
Go to the <A HREF="gperf_1.html">first</A>, <A HREF="gperf_8.html">previous</A>, <A HREF="gperf_10.html">next</A>, <A HREF="gperf_11.html">last</A> section, <A HREF="gperf_toc.html">table of contents</A>.
</BODY>