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author | Matthew Wilcox <matthew@wil.cx> | 2008-02-06 01:36:14 -0800 |
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committer | Linus Torvalds <torvalds@woody.linux-foundation.org> | 2008-02-06 10:41:00 -0800 |
commit | 4e701482d1d7b90c358e2bd244bb71623f767120 (patch) | |
tree | a054f87e31645eba4d9e2c76396c54afbe6fa895 | |
parent | d9ae90ac4bdce769ddb27c2e24c3351a30c3daf8 (diff) | |
download | linux-3.10-4e701482d1d7b90c358e2bd244bb71623f767120.tar.gz linux-3.10-4e701482d1d7b90c358e2bd244bb71623f767120.tar.bz2 linux-3.10-4e701482d1d7b90c358e2bd244bb71623f767120.zip |
hash: add explicit u32 and u64 versions of hash
The 32-bit version is more efficient (and apparently gives better hash
results than the 64-bit version), so users who are only hashing a 32-bit
quantity can now opt to use the 32-bit version explicitly, rather than
promoting to a long.
Signed-off-by: Matthew Wilcox <willy@linux.intel.com>
Cc: William Lee Irwin III <wli@holomorphy.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
-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 acf17bb8e7f..06d25c189cc 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); |