kernel / pub / scm / linux / kernel / git / axboe / fio / be26a9823261c15c6e737e2e6c8762423cf325b8 / . / hash.h

#ifndef _LINUX_HASH_H | |

#define _LINUX_HASH_H | |

#include <inttypes.h> | |

#include "arch/arch.h" | |

/* Fast hashing routine for a long. | |

(C) 2002 William Lee Irwin III, IBM */ | |

/* | |

* Knuth recommends primes in approximately golden ratio to the maximum | |

* integer representable by a machine word for multiplicative hashing. | |

* Chuck Lever verified the effectiveness of this technique: | |

* http://www.citi.umich.edu/techreports/reports/citi-tr-00-1.pdf | |

* | |

* These primes are chosen to be bit-sparse, that is operations on | |

* them can use shifts and additions instead of multiplications for | |

* machines where multiplications are slow. | |

*/ | |

#if BITS_PER_LONG == 32 | |

/* 2^31 + 2^29 - 2^25 + 2^22 - 2^19 - 2^16 + 1 */ | |

#define GOLDEN_RATIO_PRIME 0x9e370001UL | |

#elif BITS_PER_LONG == 64 | |

/* 2^63 + 2^61 - 2^57 + 2^54 - 2^51 - 2^18 + 1 */ | |

#define GOLDEN_RATIO_PRIME 0x9e37fffffffc0001UL | |

#else | |

#error Define GOLDEN_RATIO_PRIME for your wordsize. | |

#endif | |

/* | |

* The above primes are actively bad for hashing, since they are | |

* too sparse. The 32-bit one is mostly ok, the 64-bit one causes | |

* real problems. Besides, the "prime" part is pointless for the | |

* multiplicative hash. | |

* | |

* Although a random odd number will do, it turns out that the golden | |

* ratio phi = (sqrt(5)-1)/2, or its negative, has particularly nice | |

* properties. | |

* | |

* These are the negative, (1 - phi) = (phi^2) = (3 - sqrt(5))/2. | |

* (See Knuth vol 3, section 6.4, exercise 9.) | |

*/ | |

#define GOLDEN_RATIO_32 0x61C88647 | |

#define GOLDEN_RATIO_64 0x61C8864680B583EBull | |

static inline unsigned long __hash_long(uint64_t val) | |

{ | |

uint64_t hash = val; | |

#if BITS_PER_LONG == 64 | |

hash *= GOLDEN_RATIO_64; | |

#else | |

/* Sigh, gcc can't optimise this alone like it does for 32 bits. */ | |

uint64_t n = hash; | |

n <<= 18; | |

hash -= n; | |

n <<= 33; | |

hash -= n; | |

n <<= 3; | |

hash += n; | |

n <<= 3; | |

hash -= n; | |

n <<= 4; | |

hash += n; | |

n <<= 2; | |

hash += n; | |

#endif | |

return hash; | |

} | |

static inline unsigned long hash_long(unsigned long val, unsigned int bits) | |

{ | |

/* High bits are more random, so use them. */ | |

return __hash_long(val) >> (BITS_PER_LONG - bits); | |

} | |

static inline uint64_t __hash_u64(uint64_t val) | |

{ | |

return val * GOLDEN_RATIO_64; | |

} | |

static inline unsigned long hash_ptr(void *ptr, unsigned int bits) | |

{ | |

return hash_long((uintptr_t)ptr, bits); | |

} | |

/* | |

* Bob Jenkins jhash | |

*/ | |

#define JHASH_INITVAL GOLDEN_RATIO_32 | |

static inline uint32_t rol32(uint32_t word, uint32_t shift) | |

{ | |

return (word << shift) | (word >> (32 - shift)); | |

} | |

/* __jhash_mix -- mix 3 32-bit values reversibly. */ | |

#define __jhash_mix(a, b, c) \ | |

{ \ | |

a -= c; a ^= rol32(c, 4); c += b; \ | |

b -= a; b ^= rol32(a, 6); a += c; \ | |

c -= b; c ^= rol32(b, 8); b += a; \ | |

a -= c; a ^= rol32(c, 16); c += b; \ | |

b -= a; b ^= rol32(a, 19); a += c; \ | |

c -= b; c ^= rol32(b, 4); b += a; \ | |

} | |

/* __jhash_final - final mixing of 3 32-bit values (a,b,c) into c */ | |

#define __jhash_final(a, b, c) \ | |

{ \ | |

c ^= b; c -= rol32(b, 14); \ | |

a ^= c; a -= rol32(c, 11); \ | |

b ^= a; b -= rol32(a, 25); \ | |

c ^= b; c -= rol32(b, 16); \ | |

a ^= c; a -= rol32(c, 4); \ | |

b ^= a; b -= rol32(a, 14); \ | |

c ^= b; c -= rol32(b, 24); \ | |

} | |

static inline uint32_t jhash(const void *key, uint32_t length, uint32_t initval) | |

{ | |

const uint8_t *k = key; | |

uint32_t a, b, c; | |

/* Set up the internal state */ | |

a = b = c = JHASH_INITVAL + length + initval; | |

/* All but the last block: affect some 32 bits of (a,b,c) */ | |

while (length > 12) { | |

a += *k; | |

b += *(k + 4); | |

c += *(k + 8); | |

__jhash_mix(a, b, c); | |

length -= 12; | |

k += 12; | |

} | |

/* Last block: affect all 32 bits of (c) */ | |

/* All the case statements fall through */ | |

switch (length) { | |

case 12: c += (uint32_t) k[11] << 24; /* fall through */ | |

case 11: c += (uint32_t) k[10] << 16; /* fall through */ | |

case 10: c += (uint32_t) k[9] << 8; /* fall through */ | |

case 9: c += k[8]; /* fall through */ | |

case 8: b += (uint32_t) k[7] << 24; /* fall through */ | |

case 7: b += (uint32_t) k[6] << 16; /* fall through */ | |

case 6: b += (uint32_t) k[5] << 8; /* fall through */ | |

case 5: b += k[4]; /* fall through */ | |

case 4: a += (uint32_t) k[3] << 24; /* fall through */ | |

case 3: a += (uint32_t) k[2] << 16; /* fall through */ | |

case 2: a += (uint32_t) k[1] << 8; /* fall through */ | |

case 1: a += k[0]; | |

__jhash_final(a, b, c); | |

case 0: /* Nothing left to add */ | |

break; | |

} | |

return c; | |

} | |

#endif /* _LINUX_HASH_H */ |