1 .\" Copyright (c) 2001 Tobias Weingartner
2 .\" All rights reserved.
4 .\" Redistribution and use in source and binary forms, with or without
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26 .\" $OpenBSD: hash.9,v 1.5 2003/04/17 05:08:39 jmc Exp $
44 .Nd general kernel hashing functions
48 .Fn hash32_buf "const void *buf" "size_t len" "uint32_t hash"
50 .Fn hash32_str "const void *buf" "uint32_t hash"
52 .Fn hash32_strn "const void *buf" "size_t len" "uint32_t hash"
54 .Fn hash32_stre "const void *buf" "int end" "const char **ep" "uint32_t hash"
56 .Fn hash32_strne "const void *buf" "size_t len" "int end" "const char **ep" "uint32_t hash"
58 .Fn jenkins_hash "const void *buf" "size_t len" "uint32_t hash"
60 .Fn jenkins_hash32 "const uint32_t *buf" "size_t count" "uint32_t hash"
62 .Fn murmur3_32_hash "const void *buf" "size_t len" "uint32_t hash"
64 .Fn murmur3_32_hash32 "const uint32_t *buf" "size_t count" "uint32_t hash"
68 functions are used to give a consistent and general interface to
69 a decent hashing algorithm within the kernel.
70 These functions can be used to hash
73 terminated strings, as well as blocks of memory.
77 function is used as a general buffer hashing function.
80 is used to pass in the location, and
82 is the length of the buffer.
85 is used to extend an existing hash, or is passed the initial value
91 function is used to hash a
93 terminated string passed in
95 with initial hash value given in
102 function, except it also takes a
104 argument, which is the maximal length of the expected string.
110 functions are helper functions used by the kernel to hash pathname
112 These functions have the additional termination condition
113 of terminating when they find a character given by
115 in the string to be hashed.
120 it is set to the point in the buffer at which the hash function
125 function has same semantics as the
127 but provides more advanced hashing algorithm with better distribution.
131 uses same hashing algorithm as the
133 function, but works only on
135 sized arrays, thus is simplier and faster.
136 It accepts an array of
138 values in its first argument and size of this array in the second argument.
143 .Fn murmur3_32_hash32
144 functions are similar to
148 but implement the 32-bit version of MurmurHash3.
152 functions return a 32 bit hash value of the buffer or string.
154 .Bd -literal -offset indent
155 LIST_HEAD(head, cache) *hashtbl = NULL;
162 hashtbl = hashinit(numwanted, type, flags, &mask);
166 sample_use(char *str, int len)
170 hash = hash32_str(str, HASHINIT);
171 hash = hash32_buf(&len, sizeof(len), hash);
172 hashtbl[hash & mask] = len;
182 functions are only 32 bit functions.
183 They will prove to give poor 64 bit performance, especially for the
185 At the current time, this is not seen as a great limitation, as these
186 hash values are usually used to index into an array.
187 Should these hash values be used for other means, this limitation should
192 functions first appeared in
194 The current implementation of
196 functions was first committed to
198 and later imported to
202 functions were added in
206 functions were added in
211 functions were written by
212 .An Tobias Weingartner .
215 functions were written by
219 functions were written by
220 .An Dag-Erling Sm\(/orgrav Aq Mt des@FreeBSD.org .