GPERF(1) FSF 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:
Allow user to provide a string containing delimiters used to separate keywords from
their attributes. Default is ",\n".
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:
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:
Select name of the keyword component in the keyword structure.
Initializers for additional components in the keyword structure.
Specify name of generated hash function. Default is `hash'.
Specify name of generated lookup function. Default name is `in_word_set'.
Specify name of generated C++ class. Default name is `Perfect_Hash'.
Assume 7-bit characters.
Generate comparison code using strncmp rather than strcmp.
Make the contents of generated lookup tables constant, i.e., readonly.
Define constant values using an enum local to the lookup function rather than with
Include the necessary system include file <string.h> at the beginning of the code.
Generate the static table of keywords as a static global variable, rather than hid-
ing it inside of the lookup function (which is the default behavior).
Specify name of word list array. Default name is `wordlist'.
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 gener-
ated. 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.
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:
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.
Compare key lengths before trying a string comparison. This helps cut down on the
number of string comparisons made during the lookup.
Handle keywords that hash to duplicate values. This is useful for certain highly
redundant keyword sets.
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''.
Provide an initial value for the associate values array. Default is 0. Setting this
value larger helps inflate the size of the final table.
Affects the ``jump value'', i.e., how far to advance the associated character value
upon collisions. Must be an odd number, default is 5.
Do not include the length of the keyword when computing the hash function.
Reorders input keys by frequency of occurrence of the key sets. This should
decrease the search time dramatically.
Utilizes randomness to initialize the associated values table.
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 rela-
tionship to the number of keys, e.g. a value of 3 means ``allow the maximum associ-
ated 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.
Print this message.
Print the gperf version number.
Enables the debugging option (produces verbose output to the standard error).
Report bugs to <firstname.lastname@example.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
should give you access to the complete manual.
GNU gperf 2.7.2 September 2000 GPERF(1)