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Updated: Wednesday, July 27, 2022

gperf (1)


gperf - generate a perfect hash function from a key set


gperf [OPTION]... [INPUT-FILE]


GPERF(1)                              FSF                             GPERF(1)

       gperf - generate a perfect hash function from a key set

       gperf [OPTION]... [INPUT-FILE]

       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  speci-
       fied 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.

              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

       -Z, --class-name=NAME
              Specify name of generated  C++  class.  Default  name  is  'Per-

       -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.,

       -E, --enum
              Define constant values using an enum local to the  lookup  func-
              tion 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  vari-
              able, 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'.

              Use  NULL strings instead of empty strings for empty keyword ta-
              ble entries.

              Specify prefix for the constants like TOTAL_KEYWORDS.

       -W, --word-array-name=NAME
              Specify name of word list array. Default name is 'wordlist'.

              Specify name of length table array.  Default  name  is  'length-

       -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  ta-
              ble,  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 allow-
              able 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

       -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  associ-
              ated  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

       -r, --random
              Utilizes randomness to initialize the associated values table.

       -s, --size-multiple=N
              Affects  the size of the generated hash table. The numeric argu-
              ment N indicates "how many times larger or smaller" the  associ-
              ated  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 unsuccess-
              ful  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).

       Written by Douglas C. Schmidt and Bruno Haible.

       Report bugs to <bug-gperf@gnu.org>.

       Copyright (C) 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 attributes(7) for descriptions of the following attributes:

       |Availability   | developer/gperf  |
       |Stability      | Uncommitted      |

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

              info gperf

       should give you access to the complete manual.

       Source  code  for open source software components in Oracle Solaris can
       be found at https://www.oracle.com/downloads/opensource/solaris-source-

       This     software     was    built    from    source    available    at
       https://github.com/oracle/solaris-userland.   The  original   community
       source                was                downloaded                from

       Further information about this software can be found on the open source
       community website at https://www.gnu.org/software/gperf.

GNU gperf 3.1                    January 2017                         GPERF(1)