diff options
Diffstat (limited to 'include/linux/hash.h')
| -rw-r--r-- | include/linux/hash.h | 42 |
1 files changed, 27 insertions, 15 deletions
diff --git a/include/linux/hash.h b/include/linux/hash.h index acf17bb8e7f9..06d25c189cc5 100644 --- a/include/linux/hash.h +++ b/include/linux/hash.h @@ -1,6 +1,6 @@ #ifndef _LINUX_HASH_H #define _LINUX_HASH_H -/* Fast hashing routine for a long. +/* Fast hashing routine for ints, longs and pointers. (C) 2002 William Lee Irwin III, IBM */ /* @@ -13,23 +13,30 @@ * them can use shifts and additions instead of multiplications for * machines where multiplications are slow. */ -#if BITS_PER_LONG == 32 + +#include <asm/types.h> + /* 2^31 + 2^29 - 2^25 + 2^22 - 2^19 - 2^16 + 1 */ -#define GOLDEN_RATIO_PRIME 0x9e370001UL -#elif BITS_PER_LONG == 64 +#define GOLDEN_RATIO_PRIME_32 0x9e370001UL /* 2^63 + 2^61 - 2^57 + 2^54 - 2^51 - 2^18 + 1 */ -#define GOLDEN_RATIO_PRIME 0x9e37fffffffc0001UL +#define GOLDEN_RATIO_PRIME_64 0x9e37fffffffc0001UL + +#if BITS_PER_LONG == 32 +#define GOLDEN_RATIO_PRIME GOLDEN_RATIO_PRIME_32 +#define hash_long(val, bits) hash_32(val, bits) +#elif BITS_PER_LONG == 64 +#define hash_long(val, bits) hash_64(val, bits) +#define GOLDEN_RATIO_PRIME GOLDEN_RATIO_PRIME_64 #else -#error Define GOLDEN_RATIO_PRIME for your wordsize. +#error Wordsize not 32 or 64 #endif -static inline unsigned long hash_long(unsigned long val, unsigned int bits) +static inline u64 hash_64(u64 val, unsigned int bits) { - unsigned long hash = val; + u64 hash = val; -#if BITS_PER_LONG == 64 /* Sigh, gcc can't optimise this alone like it does for 32 bits. */ - unsigned long n = hash; + u64 n = hash; n <<= 18; hash -= n; n <<= 33; @@ -42,15 +49,20 @@ static inline unsigned long hash_long(unsigned long val, unsigned int bits) hash += n; n <<= 2; hash += n; -#else + + /* High bits are more random, so use them. */ + return hash >> (64 - bits); +} + +static inline u32 hash_32(u32 val, unsigned int bits) +{ /* On some cpus multiply is faster, on others gcc will do shifts */ - hash *= GOLDEN_RATIO_PRIME; -#endif + u32 hash = val * GOLDEN_RATIO_PRIME_32; /* High bits are more random, so use them. */ - return hash >> (BITS_PER_LONG - bits); + return hash >> (32 - bits); } - + static inline unsigned long hash_ptr(void *ptr, unsigned int bits) { return hash_long((unsigned long)ptr, bits); |