GPERFSection: FSF (1)
Updated: May 2007
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NAMEgperf - generate a perfect hash function from a key set
SYNOPSISgperf [OPTION]... [INPUT-FILE]
DESCRIPTIONGNU 'gperf' generates perfect hash functions.
Output file location:
- --output-file=FILE Write output to specified file.
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 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'.
- 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'.
- 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).
AUTHORWritten by Douglas C. Schmidt and Bruno Haible.
REPORTING BUGSReport bugs to <firstname.lastname@example.org>.
COPYRIGHTCopyright © 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 ALSOThe 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.
- REPORTING BUGS
- SEE ALSO