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1#ifndef _LINUX_HASH_H
2#define _LINUX_HASH_H
3/* Fast hashing routine for ints, longs and pointers.
4 (C) 2002 Nadia Yvette Chambers, IBM */
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 */
16
17#include <asm/types.h>
18#include <asm/hash.h>
19#include <linux/compiler.h>
20
21/* 2^31 + 2^29 - 2^25 + 2^22 - 2^19 - 2^16 + 1 */
22#define GOLDEN_RATIO_PRIME_32 0x9e370001UL
23/* 2^63 + 2^61 - 2^57 + 2^54 - 2^51 - 2^18 + 1 */
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
32#else
33#error Wordsize not 32 or 64
34#endif
35
36static __always_inline u64 hash_64(u64 val, unsigned int bits)
37{
38 u64 hash = val;
39
40#if defined(CONFIG_ARCH_HAS_FAST_MULTIPLIER) && BITS_PER_LONG == 64
41 hash = hash * GOLDEN_RATIO_PRIME_64;
42#else
43 /* Sigh, gcc can't optimise this alone like it does for 32 bits. */
44 u64 n = hash;
45 n <<= 18;
46 hash -= n;
47 n <<= 33;
48 hash -= n;
49 n <<= 3;
50 hash += n;
51 n <<= 3;
52 hash -= n;
53 n <<= 4;
54 hash += n;
55 n <<= 2;
56 hash += n;
57#endif
58
59 /* High bits are more random, so use them. */
60 return hash >> (64 - bits);
61}
62
63static inline u32 hash_32(u32 val, unsigned int bits)
64{
65 /* On some cpus multiply is faster, on others gcc will do shifts */
66 u32 hash = val * GOLDEN_RATIO_PRIME_32;
67
68 /* High bits are more random, so use them. */
69 return hash >> (32 - bits);
70}
71
72static inline unsigned long hash_ptr(const void *ptr, unsigned int bits)
73{
74 return hash_long((unsigned long)ptr, bits);
75}
76
77static inline u32 hash32_ptr(const void *ptr)
78{
79 unsigned long val = (unsigned long)ptr;
80
81#if BITS_PER_LONG == 64
82 val ^= (val >> 32);
83#endif
84 return (u32)val;
85}
86
87struct fast_hash_ops {
88 u32 (*hash)(const void *data, u32 len, u32 seed);
89 u32 (*hash2)(const u32 *data, u32 len, u32 seed);
90};
91
92/**
93 * arch_fast_hash - Caclulates a hash over a given buffer that can have
94 * arbitrary size. This function will eventually use an
95 * architecture-optimized hashing implementation if
96 * available, and trades off distribution for speed.
97 *
98 * @data: buffer to hash
99 * @len: length of buffer in bytes
100 * @seed: start seed
101 *
102 * Returns 32bit hash.
103 */
104extern u32 arch_fast_hash(const void *data, u32 len, u32 seed);
105
106/**
107 * arch_fast_hash2 - Caclulates a hash over a given buffer that has a
108 * size that is of a multiple of 32bit words. This
109 * function will eventually use an architecture-
110 * optimized hashing implementation if available,
111 * and trades off distribution for speed.
112 *
113 * @data: buffer to hash (must be 32bit padded)
114 * @len: number of 32bit words
115 * @seed: start seed
116 *
117 * Returns 32bit hash.
118 */
119extern u32 arch_fast_hash2(const u32 *data, u32 len, u32 seed);
120
121#endif /* _LINUX_HASH_H */