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GPERF ("1") | General commands | Unix Manual Pages | :man


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.

"Input file interpretation:"

-e, --delimiters=DELIMITER-LIST
Allow user to provide a string containing delimiters used to separate keywords from their attributes. Default is ",\n".
-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.

"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-fn-name=NAME
Specify name of generated hash function. Default is ‘hash’.
-N, --lookup-fn-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.
-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
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).
-W, --word-array-name=NAME
Specify name of word list array. Default name is ‘wordlist’.
-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 1-126, 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.
-l, --compare-strlen
Compare key lengths before trying a string comparison. This helps cut down on the number of string comparisons made during the lookup.
-D, --duplicates
Handle keywords that hash to duplicate values. This is useful for certain highly redundant keyword sets.
-f, --fast=ITERATIONS
Generate the gen-perf.hash function ‘‘fast’’. This decreases gperf’s running time at the cost of minimizing generated table size. The numeric argument represents the number of times to iterate when resolving a collision. ‘0’ means ‘‘iterate by the number of keywords’’.
-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.
-o, --occurrence-sort
Reorders input keys by frequency of occurrence of the key sets. This should decrease the search time dramatically.
-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 -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).


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