GPERF - Online Linux Manual PageSection : 1
Updated : January 2017
Source : GNU gperf 3.1
Note : FSF
NAMEgperf − generate a perfect hash function from a key set
SYNOPSISgperf [OPTION]... [INPUT-FILE]
DESCRIPTIONGNU '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).
AUTHORWritten by Douglas C. Schmidt and Bruno Haible.
REPORTING BUGSReport bugs to <bug-gperf@gnu.org>.
COPYRIGHTCopyright © 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 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. 0
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