Jens Axboe | bdc7211 | 2006-11-24 10:54:06 +0100 | [diff] [blame] | 1 | #ifndef _LINUX_HASH_H |
| 2 | #define _LINUX_HASH_H |
Jens Axboe | daaa166 | 2009-11-04 13:56:13 +0100 | [diff] [blame] | 3 | |
Jens Axboe | dadf66c | 2011-10-06 12:37:10 +0200 | [diff] [blame] | 4 | #include <inttypes.h> |
Jens Axboe | daaa166 | 2009-11-04 13:56:13 +0100 | [diff] [blame] | 5 | #include "arch/arch.h" |
| 6 | |
Jens Axboe | bdc7211 | 2006-11-24 10:54:06 +0100 | [diff] [blame] | 7 | /* Fast hashing routine for a long. |
| 8 | (C) 2002 William Lee Irwin III, IBM */ |
| 9 | |
| 10 | /* |
| 11 | * Knuth recommends primes in approximately golden ratio to the maximum |
| 12 | * integer representable by a machine word for multiplicative hashing. |
| 13 | * Chuck Lever verified the effectiveness of this technique: |
| 14 | * http://www.citi.umich.edu/techreports/reports/citi-tr-00-1.pdf |
| 15 | * |
| 16 | * These primes are chosen to be bit-sparse, that is operations on |
| 17 | * them can use shifts and additions instead of multiplications for |
| 18 | * machines where multiplications are slow. |
| 19 | */ |
Jens Axboe | 5921e80 | 2008-05-30 15:02:38 +0200 | [diff] [blame] | 20 | |
Jens Axboe | bdc7211 | 2006-11-24 10:54:06 +0100 | [diff] [blame] | 21 | #if BITS_PER_LONG == 32 |
| 22 | /* 2^31 + 2^29 - 2^25 + 2^22 - 2^19 - 2^16 + 1 */ |
| 23 | #define GOLDEN_RATIO_PRIME 0x9e370001UL |
| 24 | #elif BITS_PER_LONG == 64 |
| 25 | /* 2^63 + 2^61 - 2^57 + 2^54 - 2^51 - 2^18 + 1 */ |
| 26 | #define GOLDEN_RATIO_PRIME 0x9e37fffffffc0001UL |
| 27 | #else |
| 28 | #error Define GOLDEN_RATIO_PRIME for your wordsize. |
| 29 | #endif |
| 30 | |
Jens Axboe | ed1860c | 2012-11-07 11:39:30 +0100 | [diff] [blame^] | 31 | static inline unsigned long __hash_long(unsigned long val) |
Jens Axboe | bdc7211 | 2006-11-24 10:54:06 +0100 | [diff] [blame] | 32 | { |
| 33 | unsigned long hash = val; |
| 34 | |
| 35 | #if BITS_PER_LONG == 64 |
| 36 | /* Sigh, gcc can't optimise this alone like it does for 32 bits. */ |
| 37 | unsigned long n = hash; |
| 38 | n <<= 18; |
| 39 | hash -= n; |
| 40 | n <<= 33; |
| 41 | hash -= n; |
| 42 | n <<= 3; |
| 43 | hash += n; |
| 44 | n <<= 3; |
| 45 | hash -= n; |
| 46 | n <<= 4; |
| 47 | hash += n; |
| 48 | n <<= 2; |
| 49 | hash += n; |
| 50 | #else |
| 51 | /* On some cpus multiply is faster, on others gcc will do shifts */ |
| 52 | hash *= GOLDEN_RATIO_PRIME; |
| 53 | #endif |
| 54 | |
Jens Axboe | ed1860c | 2012-11-07 11:39:30 +0100 | [diff] [blame^] | 55 | return hash; |
| 56 | } |
| 57 | |
| 58 | static inline unsigned long hash_long(unsigned long val, unsigned int bits) |
| 59 | { |
Jens Axboe | bdc7211 | 2006-11-24 10:54:06 +0100 | [diff] [blame] | 60 | /* High bits are more random, so use them. */ |
Jens Axboe | ed1860c | 2012-11-07 11:39:30 +0100 | [diff] [blame^] | 61 | return __hash_long(val) >> (BITS_PER_LONG - bits); |
Jens Axboe | bdc7211 | 2006-11-24 10:54:06 +0100 | [diff] [blame] | 62 | } |
| 63 | |
| 64 | static inline unsigned long hash_ptr(void *ptr, unsigned int bits) |
| 65 | { |
Bruce Cran | e43606c | 2012-02-20 09:34:24 +0100 | [diff] [blame] | 66 | return hash_long((uintptr_t)ptr, bits); |
Jens Axboe | bdc7211 | 2006-11-24 10:54:06 +0100 | [diff] [blame] | 67 | } |
Jens Axboe | dadf66c | 2011-10-06 12:37:10 +0200 | [diff] [blame] | 68 | |
| 69 | /* |
| 70 | * Bob Jenkins jhash |
| 71 | */ |
| 72 | |
| 73 | #define JHASH_INITVAL GOLDEN_RATIO_PRIME |
| 74 | |
| 75 | static inline uint32_t rol32(uint32_t word, uint32_t shift) |
| 76 | { |
| 77 | return (word << shift) | (word >> (32 - shift)); |
| 78 | } |
| 79 | |
| 80 | /* __jhash_mix -- mix 3 32-bit values reversibly. */ |
| 81 | #define __jhash_mix(a, b, c) \ |
| 82 | { \ |
| 83 | a -= c; a ^= rol32(c, 4); c += b; \ |
| 84 | b -= a; b ^= rol32(a, 6); a += c; \ |
| 85 | c -= b; c ^= rol32(b, 8); b += a; \ |
| 86 | a -= c; a ^= rol32(c, 16); c += b; \ |
| 87 | b -= a; b ^= rol32(a, 19); a += c; \ |
| 88 | c -= b; c ^= rol32(b, 4); b += a; \ |
| 89 | } |
| 90 | |
| 91 | /* __jhash_final - final mixing of 3 32-bit values (a,b,c) into c */ |
| 92 | #define __jhash_final(a, b, c) \ |
| 93 | { \ |
| 94 | c ^= b; c -= rol32(b, 14); \ |
| 95 | a ^= c; a -= rol32(c, 11); \ |
| 96 | b ^= a; b -= rol32(a, 25); \ |
| 97 | c ^= b; c -= rol32(b, 16); \ |
| 98 | a ^= c; a -= rol32(c, 4); \ |
| 99 | b ^= a; b -= rol32(a, 14); \ |
| 100 | c ^= b; c -= rol32(b, 24); \ |
| 101 | } |
| 102 | |
| 103 | static inline uint32_t jhash(const void *key, uint32_t length, uint32_t initval) |
| 104 | { |
| 105 | const uint8_t *k = key; |
| 106 | uint32_t a, b, c; |
| 107 | |
| 108 | /* Set up the internal state */ |
| 109 | a = b = c = JHASH_INITVAL + length + initval; |
| 110 | |
| 111 | /* All but the last block: affect some 32 bits of (a,b,c) */ |
| 112 | while (length > 12) { |
| 113 | a += *k; |
| 114 | b += *(k + 4); |
| 115 | c += *(k + 8); |
| 116 | __jhash_mix(a, b, c); |
| 117 | length -= 12; |
| 118 | k += 12; |
| 119 | } |
| 120 | |
| 121 | /* Last block: affect all 32 bits of (c) */ |
| 122 | /* All the case statements fall through */ |
| 123 | switch (length) { |
| 124 | case 12: c += (uint32_t) k[11] << 24; |
| 125 | case 11: c += (uint32_t) k[10] << 16; |
| 126 | case 10: c += (uint32_t) k[9] << 8; |
| 127 | case 9: c += k[8]; |
| 128 | case 8: b += (uint32_t) k[7] << 24; |
| 129 | case 7: b += (uint32_t) k[6] << 16; |
| 130 | case 6: b += (uint32_t) k[5] << 8; |
| 131 | case 5: b += k[4]; |
| 132 | case 4: a += (uint32_t) k[3] << 24; |
| 133 | case 3: a += (uint32_t) k[2] << 16; |
| 134 | case 2: a += (uint32_t) k[1] << 8; |
| 135 | case 1: a += k[0]; |
| 136 | __jhash_final(a, b, c); |
| 137 | case 0: /* Nothing left to add */ |
| 138 | break; |
| 139 | } |
| 140 | |
| 141 | return c; |
| 142 | } |
| 143 | |
Jens Axboe | bdc7211 | 2006-11-24 10:54:06 +0100 | [diff] [blame] | 144 | #endif /* _LINUX_HASH_H */ |