GPERF(1) FSF GPERF(1)NAMEgperf - generate a perfect hash function from a key set
SYNOPSISgperf [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 delim
iters used to separate keywords from their
attributes. Default is ",\n".
-t, --struct-type
Allows the user to include a structured type decla
ration 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 key
word 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 con
stant, 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 behav
ior).
-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 state
ment 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.
-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, inclu
sive. 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 posi
tions, 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 compari
son. 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 mini
mizing 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 colli
sions. Must be an odd number, default is 5.
-n, --no-strlen
Do not include the length of the keyword when com
puting 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 associ
ated value to be about 3 times larger than the num
ber 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 out
put to the standard error).
REPORTING BUGS
Report bugs to <bug-gnu-utils@gnu.org>.
SEE ALSO
The full documentation for gperf is maintained as a Tex
info 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.
GNU gperf 2.7.2 September 2000 GPERF(1)
