gperf
The perfect hash function generator gperf reads a set of
"keywords" from a keyfile (or from the standard input by
default). It attempts to derive a perfect hashing function that
recognizes a member of the static keyword set with at most a
single probe into the lookup table. If gperf 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 gperf.
By default, gperf 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 gperf to utilize a C switch
statement scheme that minimizes data space storage size. Furthermore,
using a C switch may actually speed up the keyword retrieval time
somewhat. Actual results depend on your C compiler, of course.
In general, gperf assigns values to the characters it is using
for hashing until some set of values gives each keyword a unique value.
A helpful heuristic is that the larger the hash value range, the easier
it is for gperf to find and generate a perfect hash function.
Experimentation is the key to getting the most from gperf.
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