1GPERF(1) FSF GPERF(1)
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6 gperf - generate a perfect hash function from a key set
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9 gperf [OPTION]... [INPUT-FILE]
10
12 GNU 'gperf' generates perfect hash functions.
13 If a long option shows an argument as mandatory, then it is mandatory
15 for the equivalent short option also.
16 Output file location:
18 --output-file=FILE Write output to specified file.
19 The results are written to standard output if no output file is speci‐
21 fied or if it is -.
22 Input file interpretation:
24 -e, --delimiters=DELIMITER-LIST
25 Allow user to provide a string containing delimiters used to
26 separate keywords from their attributes. Default is ",".
27 -t, --struct-type
29 Allows the user to include a structured type declaration for
30 generated code. Any text before %% is considered part of the
31 type declaration. Key words and additional fields may follow
32 this, one group of fields per line.
33 --ignore-case
35 Consider upper and lower case ASCII characters as equivalent.
36 Note that locale dependent case mappings are ignored.
37 Language for the output code:
39 -L, --language=LANGUAGE-NAME
40 Generates code in the specified language. Languages handled are
41 currently C++, ANSI-C, C, and KR-C. The default is ANSI-C.
42 Details in the output code:
44 -K, --slot-name=NAME
45 Select name of the keyword component in the keyword structure.
46 -F, --initializer-suffix=INITIALIZERS
48 Initializers for additional components in the keyword structure.
49 -H, --hash-function-name=NAME
51 Specify name of generated hash function. Default is 'hash'.
52 -N, --lookup-function-name=NAME
54 Specify name of generated lookup function. Default name is
55 'in_word_set'.
56 -Z, --class-name=NAME
58 Specify name of generated C++ class. Default name is 'Per‐
59 fect_Hash'.
60 -7, --seven-bit
62 Assume 7-bit characters.
63 -l, --compare-lengths
65 Compare key lengths before trying a string comparison. This is
66 necessary if the keywords contain NUL bytes. It also helps cut
67 down on the number of string comparisons made during the lookup.
68 -c, --compare-strncmp
70 Generate comparison code using strncmp rather than strcmp.
71 -C, --readonly-tables
73 Make the contents of generated lookup tables constant, i.e.,
74 readonly.
75 -E, --enum
77 Define constant values using an enum local to the lookup func‐
78 tion rather than with defines.
79 -I, --includes
81 Include the necessary system include file <string.h> at the
82 beginning of the code.
83 -G, --global-table
85 Generate the static table of keywords as a static global vari‐
86 able, rather than hiding it inside of the lookup function (which
87 is the default behavior).
88 -P, --pic
90 Optimize the generated table for inclusion in shared libraries.
91 This reduces the startup time of programs using a shared library
92 containing the generated code.
93 -Q, --string-pool-name=NAME
95 Specify name of string pool generated by option --pic. Default
96 name is 'stringpool'.
97 --null-strings
99 Use NULL strings instead of empty strings for empty keyword ta‐
100 ble entries.
101 --constants-prefix=PREFIX
103 Specify prefix for the constants like TOTAL_KEYWORDS.
104 -W, --word-array-name=NAME
106 Specify name of word list array. Default name is 'wordlist'.
107 --length-table-name=NAME
109 Specify name of length table array. Default name is 'length‐
110 table'.
111 -S, --switch=COUNT
113 Causes the generated C code to use a switch statement scheme,
114 rather than an array lookup table. This can lead to a reduction
115 in both time and space requirements for some keyfiles. The COUNT
116 argument determines how many switch statements are generated. A
117 value of 1 generates 1 switch containing all the elements, a
118 value of 2 generates 2 tables with 1/2 the elements in each ta‐
119 ble, etc. If COUNT is very large, say 1000000, the generated C
120 code does a binary search.
121 -T, --omit-struct-type
123 Prevents the transfer of the type declaration to the output
124 file. Use this option if the type is already defined elsewhere.
125 Algorithm employed by gperf:
127 -k, --key-positions=KEYS
128 Select the key positions used in the hash function. The allow‐
129 able choices range between 1-255, inclusive. The positions are
130 separated by commas, ranges may be used, and key positions may
131 occur in any order. Also, the meta-character '*' causes the
132 generated hash function to consider ALL key positions, and $
133 indicates the "final character" of a key, e.g., $,1,2,4,6-10.
134 -D, --duplicates
136 Handle keywords that hash to duplicate values. This is useful
137 for certain highly redundant keyword sets.
138 -m, --multiple-iterations=ITERATIONS
140 Perform multiple choices of the -i and -j values, and choose the
141 best results. This increases the running time by a factor of
142 ITERATIONS but does a good job minimizing the generated table
143 size.
144 -i, --initial-asso=N
146 Provide an initial value for the associate values array. Default
147 is 0. Setting this value larger helps inflate the size of the
148 final table.
149 -j, --jump=JUMP-VALUE
151 Affects the "jump value", i.e., how far to advance the associ‐
152 ated character value upon collisions. Must be an odd number,
153 default is 5.
154 -n, --no-strlen
156 Do not include the length of the keyword when computing the hash
157 function.
158 -r, --random
160 Utilizes randomness to initialize the associated values table.
161 -s, --size-multiple=N
163 Affects the size of the generated hash table. The numeric argu‐
164 ment N indicates "how many times larger or smaller" the associ‐
165 ated value range should be, in relationship to the number of
166 keys, e.g. a value of 3 means "allow the maximum associated
167 value to be about 3 times larger than the number of input keys".
168 Conversely, a value of 1/3 means "make the maximum associated
169 value about 3 times smaller than the number of input keys". A
170 larger table should decrease the time required for an unsuccess‐
171 ful search, at the expense of extra table space. Default value
172 is 1.
173 Informative output:
175 -h, --help
176 Print this message.
177 -v, --version
179 Print the gperf version number.
180 -d, --debug
182 Enables the debugging option (produces verbose output to the
183 standard error).
184
186 Written by Douglas C. Schmidt and Bruno Haible.
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189 Report bugs to <bug-gperf@gnu.org>.
190
192 Copyright © 1989-2017 Free Software Foundation, Inc. License GPLv3+:
193 GNU GPL version 3 or later <http://gnu.org/licenses/gpl.html>
194 This is free software: you are free to change and redistribute it.
195 There is NO WARRANTY, to the extent permitted by law.
196
198 The full documentation for gperf is maintained as a Texinfo manual. If
199 the info and gperf programs are properly installed at your site, the
200 command
201 info gperf
203 should give you access to the complete manual.
205GNU gperf 3.1 January 2017 GPERF(1)