Ubuntu Manpage: gperf - generate a perfect hash function from a key set

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 -.

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).

AUTHOR

       Written by Douglas C. Schmidt and Bruno Haible.

REPORTING BUGS

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

COPYRIGHT