Make ARCH_HAS_FAST_MULTIPLIER a real config variable
[linux-2.6-block.git] / include / linux / hash.h
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1da177e4
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1#ifndef _LINUX_HASH_H
2#define _LINUX_HASH_H
4e701482 3/* Fast hashing routine for ints, longs and pointers.
6d49e352 4 (C) 2002 Nadia Yvette Chambers, IBM */
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5
6/*
7 * Knuth recommends primes in approximately golden ratio to the maximum
8 * integer representable by a machine word for multiplicative hashing.
9 * Chuck Lever verified the effectiveness of this technique:
10 * http://www.citi.umich.edu/techreports/reports/citi-tr-00-1.pdf
11 *
12 * These primes are chosen to be bit-sparse, that is operations on
13 * them can use shifts and additions instead of multiplications for
14 * machines where multiplications are slow.
15 */
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16
17#include <asm/types.h>
71ae8aac 18#include <asm/hash.h>
65c10553 19#include <linux/compiler.h>
4e701482 20
1da177e4 21/* 2^31 + 2^29 - 2^25 + 2^22 - 2^19 - 2^16 + 1 */
4e701482 22#define GOLDEN_RATIO_PRIME_32 0x9e370001UL
1da177e4 23/* 2^63 + 2^61 - 2^57 + 2^54 - 2^51 - 2^18 + 1 */
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24#define GOLDEN_RATIO_PRIME_64 0x9e37fffffffc0001UL
25
26#if BITS_PER_LONG == 32
27#define GOLDEN_RATIO_PRIME GOLDEN_RATIO_PRIME_32
28#define hash_long(val, bits) hash_32(val, bits)
29#elif BITS_PER_LONG == 64
30#define hash_long(val, bits) hash_64(val, bits)
31#define GOLDEN_RATIO_PRIME GOLDEN_RATIO_PRIME_64
1da177e4 32#else
4e701482 33#error Wordsize not 32 or 64
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34#endif
35
65c10553 36static __always_inline u64 hash_64(u64 val, unsigned int bits)
1da177e4 37{
4e701482 38 u64 hash = val;
1da177e4 39
1da177e4 40 /* Sigh, gcc can't optimise this alone like it does for 32 bits. */
4e701482 41 u64 n = hash;
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42 n <<= 18;
43 hash -= n;
44 n <<= 33;
45 hash -= n;
46 n <<= 3;
47 hash += n;
48 n <<= 3;
49 hash -= n;
50 n <<= 4;
51 hash += n;
52 n <<= 2;
53 hash += n;
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54
55 /* High bits are more random, so use them. */
56 return hash >> (64 - bits);
57}
58
59static inline u32 hash_32(u32 val, unsigned int bits)
60{
1da177e4 61 /* On some cpus multiply is faster, on others gcc will do shifts */
4e701482 62 u32 hash = val * GOLDEN_RATIO_PRIME_32;
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63
64 /* High bits are more random, so use them. */
4e701482 65 return hash >> (32 - bits);
1da177e4 66}
4e701482 67
f9918794 68static inline unsigned long hash_ptr(const void *ptr, unsigned int bits)
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69{
70 return hash_long((unsigned long)ptr, bits);
71}
b14f243a
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72
73static inline u32 hash32_ptr(const void *ptr)
74{
75 unsigned long val = (unsigned long)ptr;
76
77#if BITS_PER_LONG == 64
78 val ^= (val >> 32);
79#endif
80 return (u32)val;
81}
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82
83struct fast_hash_ops {
84 u32 (*hash)(const void *data, u32 len, u32 seed);
85 u32 (*hash2)(const u32 *data, u32 len, u32 seed);
86};
87
88/**
89 * arch_fast_hash - Caclulates a hash over a given buffer that can have
90 * arbitrary size. This function will eventually use an
91 * architecture-optimized hashing implementation if
92 * available, and trades off distribution for speed.
93 *
94 * @data: buffer to hash
95 * @len: length of buffer in bytes
96 * @seed: start seed
97 *
98 * Returns 32bit hash.
99 */
100extern u32 arch_fast_hash(const void *data, u32 len, u32 seed);
101
102/**
103 * arch_fast_hash2 - Caclulates a hash over a given buffer that has a
104 * size that is of a multiple of 32bit words. This
105 * function will eventually use an architecture-
106 * optimized hashing implementation if available,
107 * and trades off distribution for speed.
108 *
109 * @data: buffer to hash (must be 32bit padded)
110 * @len: number of 32bit words
111 * @seed: start seed
112 *
113 * Returns 32bit hash.
114 */
115extern u32 arch_fast_hash2(const u32 *data, u32 len, u32 seed);
116
1da177e4 117#endif /* _LINUX_HASH_H */