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#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
static inline unsigned long hash_long(unsigned long val, unsigned int bits)
{
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
/* High bits are more random, so use them. */
return hash >> (BITS_PER_LONG - bits);
}
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 */
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