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1da177e4 LT |
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 */ |
1da177e4 LT |
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 | */ | |
4e701482 MW |
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 */ |
4e701482 MW |
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 |
1da177e4 LT |
34 | #endif |
35 | ||
65c10553 | 36 | static __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; |
1da177e4 LT |
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; | |
4e701482 MW |
54 | |
55 | /* High bits are more random, so use them. */ | |
56 | return hash >> (64 - bits); | |
57 | } | |
58 | ||
59 | static 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; |
1da177e4 LT |
63 | |
64 | /* High bits are more random, so use them. */ | |
4e701482 | 65 | return hash >> (32 - bits); |
1da177e4 | 66 | } |
4e701482 | 67 | |
f9918794 | 68 | static inline unsigned long hash_ptr(const void *ptr, unsigned int bits) |
1da177e4 LT |
69 | { |
70 | return hash_long((unsigned long)ptr, bits); | |
71 | } | |
b14f243a PE |
72 | |
73 | static 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 | } | |
71ae8aac FF |
82 | |
83 | struct 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 | */ | |
100 | extern 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 | */ | |
115 | extern u32 arch_fast_hash2(const u32 *data, u32 len, u32 seed); | |
116 | ||
1da177e4 | 117 | #endif /* _LINUX_HASH_H */ |