GNU/Linux |
CentOS 3.3 |
|
gperf(1) |
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).
Report bugs to <bug-gnu-utils@gnu.org>.
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.
gperf(1) |