gperf - generate a perfect hash function from a key set

NAME  SYNOPSIS  DESCRIPTION  Output file location:  Input file interpretation:  Language for the output code:  Details in the output code:  Algorithm employed by gperf:  Informative output:  AUTHOR  REPORTING BUGS  COPYRIGHT  SEE ALSO 

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 delimiters used to separate keywords from their attributes. Default is ",".

−t, −−struct−type

Allows the user to include a structured type declaration 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 mappings are ignored.

Language for the output code:

−L, −−language=LANGUAGE−NAME

Generates code in the specified language. Languages handled are currently C++, ANSI-C, C, and KR-C. The default is ANSI-C.

Details in the output code:

−K, −−slot−name=NAME

Select name of the keyword component in the keyword 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 comparison. This is necessary if the keywords contain 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 constant, 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 behavior).

−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.

−−constants−prefix=PREFIX

Specify prefix for the constants like TOTAL_KEYWORDS.

−W, −−word−array−name=NAME

Specify name of word list array. Default name is ’wordlist’.

−−length−table−name=NAME

Specify name of length table array. Default name is ’lengthtable’.

−S, −−switch=COUNT

Causes the generated C code to use a switch statement scheme, rather than an array lookup table. This can lead to a reduction in both time and space requirements for some keyfiles. The COUNT argument determines how many switch statements 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 function. The allowable choices range between 1-255, inclusive. The positions are separated by commas, 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 keyword 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 collisions. 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 associated 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 <[email protected]>.

COPYRIGHT

Copyright © 1989-2017 Free Software Foundation, Inc. License GPLv3+: GNU GPL version 3 or later <http://gnu.org/licenses/gpl.html>
This is free software: you are free to change and redistribute it. There is NO WARRANTY, to the extent permitted by law.

SEE ALSO

The full documentation for gperf is maintained as a Texinfo manual. If the info and gperf programs are properly installed at your site, the command

info gperf

should give you access to the complete manual.


Updated 2024-01-29 - jenkler.se | uex.se