1 .\" Copyright (c) 2001 Tobias Weingartner
2 .\" All rights reserved.
4 .\" Redistribution and use in source and binary forms, with or without
5 .\" modification, are permitted provided that the following conditions
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15 .\" THIS SOFTWARE IS PROVIDED BY THE AUTHOR ``AS IS'' AND ANY EXPRESS OR
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26 .\" $OpenBSD: hash.9,v 1.5 2003/04/17 05:08:39 jmc Exp $
34 .\" XXX - Should all these be .Nm as well?
41 .Nd general kernel hashing functions
43 .Fd #include <sys/hash.h>
45 .Fn hash32_buf "void *buf" "size_t len" "uint32_t hash"
47 .Fn hash32_str "void *buf" "uint32_t hash"
49 .Fn hash32_strn "void *buf" "size_t len" "uint32_t hash"
51 .Fn hash32_stre "void *buf" "int end" "char **ep" "uint32_t hash"
53 .Fn hash32_strne "void *buf" "size_t len" "int end" "char **ep" "uint32_t hash"
57 functions are used to give a consistent and general interface to
58 a decent hashing algorithm within the kernel.
59 These functions can be used to hash ASCII
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;
122 hashtbl = hashinit(numwanted, type, flags, &mask);
126 sample_use(char *str, int len)
130 hash = hash32_str(str, HASHINIT);
131 hash = hash32_buf(&len, sizeof(len), hash);
132 hashtbl[hash & mask] = len;
142 functions are only 32 bit functions.
143 They will prove to give poor 64 bit performance, especially for the
145 At the current time, this is not seen as a great limitation, as these
146 hash values are usually used to index into an array.
147 Should these hash values be used for other means, this limitation should
152 functions were first committed to
156 versions were written and massaged for
158 by Tobias Weingartner,
159 and finally committed for