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=FILE Write output to specified
file.
The results are written to standard output if no output file is
specified or if it is -.
- -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.
- -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.
- -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.
- -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.
Written by Douglas C. Schmidt and Bruno Haible.
Report bugs to <bug-gperf@gnu.org>.
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.
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.