| #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 |
| |
| #define GR_PRIME_64 0x9e37fffffffc0001ULL |
| |
| static inline unsigned long __hash_long(unsigned long val) |
| { |
| unsigned long hash = val; |
| |
| #if BITS_PER_LONG == 64 |
| /* Sigh, gcc can't optimise this alone like it does for 32 bits. */ |
| unsigned long 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; |
| #else |
| /* On some cpus multiply is faster, on others gcc will do shifts */ |
| hash *= GOLDEN_RATIO_PRIME; |
| #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 * GR_PRIME_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_PRIME |
| |
| 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; |
| case 11: c += (uint32_t) k[10] << 16; |
| case 10: c += (uint32_t) k[9] << 8; |
| case 9: c += k[8]; |
| case 8: b += (uint32_t) k[7] << 24; |
| case 7: b += (uint32_t) k[6] << 16; |
| case 6: b += (uint32_t) k[5] << 8; |
| case 5: b += k[4]; |
| case 4: a += (uint32_t) k[3] << 24; |
| case 3: a += (uint32_t) k[2] << 16; |
| case 2: a += (uint32_t) k[1] << 8; |
| case 1: a += k[0]; |
| __jhash_final(a, b, c); |
| case 0: /* Nothing left to add */ |
| break; |
| } |
| |
| return c; |
| } |
| |
| #endif /* _LINUX_HASH_H */ |