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 -.
- -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 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.
- -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.
- -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 © 1989-1998, 2000-2004, 2006-2007 Free Software Foundation, Inc.
This is free software; see the source for copying conditions. There is NO
warranty; not even for MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.
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.