1 #ifndef _LINUX_HASH_H 2 #define _LINUX_HASH_H 3 4 #include <inttypes.h> 5 #include "arch/arch.h" 6 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 */ 20 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 31 #define GR_PRIME_64 0x9e37fffffffc0001ULL 32 33 static inline unsigned long __hash_long(unsigned long val) 34 { 35 unsigned long hash = val; 36 37 #if BITS_PER_LONG == 64 38 /* Sigh, gcc can't optimise this alone like it does for 32 bits. */ 39 unsigned long n = hash; 40 n <<= 18; 41 hash -= n; 42 n <<= 33; 43 hash -= n; 44 n <<= 3; 45 hash += n; 46 n <<= 3; 47 hash -= n; 48 n <<= 4; 49 hash += n; 50 n <<= 2; 51 hash += n; 52 #else 53 /* On some cpus multiply is faster, on others gcc will do shifts */ 54 hash *= GOLDEN_RATIO_PRIME; 55 #endif 56 57 return hash; 58 } 59 60 static inline unsigned long hash_long(unsigned long val, unsigned int bits) 61 { 62 /* High bits are more random, so use them. */ 63 return __hash_long(val) >> (BITS_PER_LONG - bits); 64 } 65 66 static inline uint64_t __hash_u64(uint64_t val) 67 { 68 return val * GR_PRIME_64; 69 } 70 71 static inline unsigned long hash_ptr(void *ptr, unsigned int bits) 72 { 73 return hash_long((uintptr_t)ptr, bits); 74 } 75 76 /* 77 * Bob Jenkins jhash 78 */ 79 80 #define JHASH_INITVAL GOLDEN_RATIO_PRIME 81 82 static inline uint32_t rol32(uint32_t word, uint32_t shift) 83 { 84 return (word << shift) | (word >> (32 - shift)); 85 } 86 87 /* __jhash_mix -- mix 3 32-bit values reversibly. */ 88 #define __jhash_mix(a, b, c) \ 89 { \ 90 a -= c; a ^= rol32(c, 4); c += b; \ 91 b -= a; b ^= rol32(a, 6); a += c; \ 92 c -= b; c ^= rol32(b, 8); b += a; \ 93 a -= c; a ^= rol32(c, 16); c += b; \ 94 b -= a; b ^= rol32(a, 19); a += c; \ 95 c -= b; c ^= rol32(b, 4); b += a; \ 96 } 97 98 /* __jhash_final - final mixing of 3 32-bit values (a,b,c) into c */ 99 #define __jhash_final(a, b, c) \ 100 { \ 101 c ^= b; c -= rol32(b, 14); \ 102 a ^= c; a -= rol32(c, 11); \ 103 b ^= a; b -= rol32(a, 25); \ 104 c ^= b; c -= rol32(b, 16); \ 105 a ^= c; a -= rol32(c, 4); \ 106 b ^= a; b -= rol32(a, 14); \ 107 c ^= b; c -= rol32(b, 24); \ 108 } 109 110 static inline uint32_t jhash(const void *key, uint32_t length, uint32_t initval) 111 { 112 const uint8_t *k = key; 113 uint32_t a, b, c; 114 115 /* Set up the internal state */ 116 a = b = c = JHASH_INITVAL + length + initval; 117 118 /* All but the last block: affect some 32 bits of (a,b,c) */ 119 while (length > 12) { 120 a += *k; 121 b += *(k + 4); 122 c += *(k + 8); 123 __jhash_mix(a, b, c); 124 length -= 12; 125 k += 12; 126 } 127 128 /* Last block: affect all 32 bits of (c) */ 129 /* All the case statements fall through */ 130 switch (length) { 131 case 12: c += (uint32_t) k[11] << 24; 132 case 11: c += (uint32_t) k[10] << 16; 133 case 10: c += (uint32_t) k[9] << 8; 134 case 9: c += k[8]; 135 case 8: b += (uint32_t) k[7] << 24; 136 case 7: b += (uint32_t) k[6] << 16; 137 case 6: b += (uint32_t) k[5] << 8; 138 case 5: b += k[4]; 139 case 4: a += (uint32_t) k[3] << 24; 140 case 3: a += (uint32_t) k[2] << 16; 141 case 2: a += (uint32_t) k[1] << 8; 142 case 1: a += k[0]; 143 __jhash_final(a, b, c); 144 case 0: /* Nothing left to add */ 145 break; 146 } 147 148 return c; 149 } 150 151 #endif /* _LINUX_HASH_H */ 152
