gperf
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.
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).
REPORTING BUGS
Report bugs to <bug-gnu-utils@gnu.org>.
SEE ALSO
