1 .\" Copyright (c) 2001 Tobias Weingartner
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26 .\" $OpenBSD: hash.9,v 1.5 2003/04/17 05:08:39 jmc Exp $
42 .Nd general kernel hashing functions
46 .Fn hash32_buf "const void *buf" "size_t len" "uint32_t hash"
48 .Fn hash32_str "const void *buf" "uint32_t hash"
50 .Fn hash32_strn "const void *buf" "size_t len" "uint32_t hash"
52 .Fn hash32_stre "const void *buf" "int end" "const char **ep" "uint32_t hash"
54 .Fn hash32_strne "const void *buf" "size_t len" "int end" "const char **ep" "uint32_t hash"
56 .Fn jenkins_hash "const void *buf" "size_t len" "uint32_t hash"
58 .Fn jenkins_hash32 "const uint32_t *buf" "size_t count" "uint32_t hash"
62 functions are used to give a consistent and general interface to
63 a decent hashing algorithm within the kernel.
64 These functions can be used to hash
67 terminated strings, as well as blocks of memory.
71 function is used as a general buffer hashing function.
74 is used to pass in the location, and
76 is the length of the buffer.
79 is used to extend an existing hash, or is passed the initial value
85 function is used to hash a
87 terminated string passed in
89 with initial hash value given in
96 function, except it also takes a
98 argument, which is the maximal length of the expected string.
104 functions are helper functions used by the kernel to hash pathname
106 These functions have the additional termination condition
107 of terminating when they find a character given by
109 in the string to be hashed.
114 it is set to the point in the buffer at which the hash function
119 function has same semantics as the
121 but provides more advanced hashing algorithm with better distribution.
125 uses same hashing algorithm as the
127 function, but works only on
129 sized arrays, thus is simpler and faster.
130 It accepts an array of
132 values in its first argument and size of this array in the second argument.
136 functions return a 32 bit hash value of the buffer or string.
138 .Bd -literal -offset indent
139 LIST_HEAD(head, cache) *hashtbl = NULL;
146 hashtbl = hashinit(numwanted, type, flags, &mask);
150 sample_use(char *str, int len)
154 hash = hash32_str(str, HASHINIT);
155 hash = hash32_buf(&len, sizeof(len), hash);
156 hashtbl[hash & mask] = len;
166 functions are only 32 bit functions.
167 They will prove to give poor 64 bit performance, especially for the
169 At the current time, this is not seen as a great limitation, as these
170 hash values are usually used to index into an array.
171 Should these hash values be used for other means, this limitation should
176 functions first appeared in
178 The current implementation of
180 functions was first committed to
182 and later imported to
186 functions were added in
191 functions were written by
192 .An Tobias Weingartner .
195 functions was written by