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GPERF(1) FSF GPERF(1)
NAME
gperf - generate a perfect hash function from a key set
SYNOPSIS
gperf [OPTION]... [INPUT-FILE]
DESCRIPTION
GNU 'gperf' generates perfect hash functions.
If a long option shows an argument as mandatory, then it
is mandatory for the equivalent short option also.
Output file location:
--output-file=FILE Write output to specified file.
The results are written to standard output if no output
file is specified or if it is -.
Input file interpretation:
-e, --delimiters=DELIMITER-LIST
Allow user to provide a string containing delim-
iters used to separate keywords from their
attributes. Default is ",".
-t, --struct-type
Allows the user to include a structured type dec-
laration for generated code. Any text before %%
is considered part of the type declaration. Key
words and additional fields may follow this, one
group of fields per line.
--ignore-case
Consider upper and lower case ASCII characters as
equivalent. Note that locale dependent case map-
pings are ignored.
Language for the output code:
-L, --language=LANGUAGE-NAME
Generates code in the specified language. Lan-
guages handled are currently C++, ANSI-C, C, and
KR-C. The default is C.
Details in the output code:
-K, --slot-name=NAME
Select name of the keyword component in the key-
word structure.
-F, --initializer-suffix=INITIALIZERS
Initializers for additional components in the
keyword structure.
-H, --hash-function-name=NAME
Specify name of generated hash function. Default
is 'hash'.
-N, --lookup-function-name=NAME
Specify name of generated lookup function.
Default name is 'in_word_set'.
-Z, --class-name=NAME
Specify name of generated C++ class. Default name
is 'Perfect_Hash'.
-7, --seven-bit
Assume 7-bit characters.
-l, --compare-lengths
Compare key lengths before trying a string com-
parison. This is necessary if the keywords con-
tain NUL bytes. It also helps cut down on the
number of string comparisons made during the
lookup.
-c, --compare-strncmp
Generate comparison code using strncmp rather
than strcmp.
-C, --readonly-tables
Make the contents of generated lookup tables con-
stant, i.e., readonly.
-E, --enum
Define constant values using an enum local to the
lookup function rather than with defines.
-I, --includes
Include the necessary system include file
<string.h> at the beginning of the code.
-G, --global-table
Generate the static table of keywords as a static
global variable, rather than hiding it inside of
the lookup function (which is the default behav-
ior).
-P, --pic
Optimize the generated table for inclusion in
shared libraries. This reduces the startup time
of programs using a shared library containing the
generated code.
-Q, --string-pool-name=NAME
Specify name of string pool generated by option
--pic. Default name is 'stringpool'.
--null-strings
Use NULL strings instead of empty strings for
empty keyword table entries.
-W, --word-array-name=NAME
Specify name of word list array. Default name is
'wordlist'.
-S, --switch=COUNT
Causes the generated C code to use a switch
statement scheme, rather than an array lookup ta-
ble. This can lead to a reduction in both time
and space requirements for some keyfiles. The
COUNT argument determines how many switch state-
ments are generated. A value of 1 generates 1
switch containing all the elements, a value of 2
generates 2 tables with 1/2 the elements in each
table, etc. If COUNT is very large, say 1000000,
the generated C code does a binary search.
-T, --omit-struct-type
Prevents the transfer of the type declaration to
the output file. Use this option if the type is
already defined elsewhere.
Algorithm employed by gperf:
-k, --key-positions=KEYS
Select the key positions used in the hash func-
tion. The allowable choices range between 1-255,
inclusive. The positions are separated by com-
mas, ranges may be used, and key positions may
occur in any order. Also, the meta-character '*'
causes the generated hash function to consider
ALL key positions, and $ indicates the "final
character" of a key, e.g., $,1,2,4,6-10.
-D, --duplicates
Handle keywords that hash to duplicate values.
This is useful for certain highly redundant key-
word sets.
-m, --multiple-iterations=ITERATIONS
Perform multiple choices of the -i and -j values,
and choose the best results. This increases the
running time by a factor of ITERATIONS but does a
good job minimizing the generated table size.
-i, --initial-asso=N
Provide an initial value for the associate values
array. Default is 0. Setting this value larger
helps inflate the size of the final table.
-j, --jump=JUMP-VALUE
Affects the "jump value", i.e., how far to
advance the associated character value upon col-
lisions. Must be an odd number, default is 5.
-n, --no-strlen
Do not include the length of the keyword when
computing the hash function.
-r, --random
Utilizes randomness to initialize the associated
values table.
-s, --size-multiple=N
Affects the size of the generated hash table. The
numeric argument N indicates "how many times
larger or smaller" the associated value range
should be, in relationship to the number of keys,
e.g. a value of 3 means "allow the maximum asso-
ciated value to be about 3 times larger than the
number of input keys". Conversely, a value of 1/3
means "make the maximum associated value about 3
times smaller than the number of input keys". A
larger table should decrease the time required
for an unsuccessful search, at the expense of
extra table space. Default value is 1.
Informative output:
-h, --help
Print this message.
-v, --version
Print the gperf version number.
-d, --debug
Enables the debugging option (produces verbose
output to the standard error).
AUTHOR
Written by Douglas C. Schmidt and Bruno Haible.
REPORTING BUGS
Report bugs to <bug-gnu-gperf@gnu.org>.
COPYRIGHT
Copyright (C) 1989-1998, 2000-2003 Free Software Founda-
tion, Inc.
This is free software; see the source for copying condi-
tions. There is NO warranty; not even for MERCHANTABIL-
ITY or FITNESS FOR A PARTICULAR PURPOSE.
SEE ALSO
The full documentation for gperf is maintained as a Tex-
info manual. If the info and gperf programs are prop-
erly installed at your site, the command
info gperf
should give you access to the complete manual.
GNU gperf 3.0.1 June 2003 GPERF(1)
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