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 $
40 .Nd general kernel hashing functions
44 .Fn hash32_buf "const void *buf" "size_t len" "uint32_t hash"
46 .Fn hash32_str "const void *buf" "uint32_t hash"
48 .Fn hash32_strn "const void *buf" "size_t len" "uint32_t hash"
50 .Fn hash32_stre "const void *buf" "int end" "char **ep" "uint32_t hash"
52 .Fn hash32_strne "const void *buf" "size_t len" "int end" "char **ep" "uint32_t hash"
56 functions are used to give a consistent and general interface to
57 a decent hashing algorithm within the kernel.
58 These functions can be used to hash
61 terminated strings, as well as blocks of memory.
65 function is used as a general buffer hashing function.
68 is used to pass in the location, and
70 is the length of the buffer.
73 is used to extend an existing hash, or is passed the initial value
79 function is used to hash a
81 terminated string passed in
83 with initial hash value given in
90 function, except it also takes a
92 argument, which is the maximal length of the expected string.
98 functions are helper functions used by the kernel to hash pathname
100 These functions have the additional termination condition
101 of terminating when they find a character given by
103 in the string to be hashed.
108 it is set to the point in the buffer at which the hash function
113 functions return a 32 bit hash value of the buffer or string.
115 .Bd -literal -offset indent
116 LIST_HEAD(head, cache) *hashtbl = NULL;
123 hashtbl = hashinit(numwanted, type, flags, &mask);
127 sample_use(char *str, int len)
131 hash = hash32_str(str, HASHINIT);
132 hash = hash32_buf(&len, sizeof(len), hash);
133 hashtbl[hash & mask] = len;
143 functions are only 32 bit functions.
144 They will prove to give poor 64 bit performance, especially for the
146 At the current time, this is not seen as a great limitation, as these
147 hash values are usually used to index into an array.
148 Should these hash values be used for other means, this limitation should
153 functions were first committed to
157 versions were written and massaged for
159 by Tobias Weingartner,
160 and finally committed for