[linux.git] / include / linux / hash.h

#ifndef _LINUX_HASH_H
#define _LINUX_HASH_H
/* Fast hashing routine for ints,  longs and pointers.
   (C) 2002 Nadia Yvette Chambers, 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.
 */

#include <asm/types.h>
#include <linux/compiler.h>

/* 2^31 + 2^29 - 2^25 + 2^22 - 2^19 - 2^16 + 1 */
#define GOLDEN_RATIO_PRIME_32 0x9e370001UL
/*  2^63 + 2^61 - 2^57 + 2^54 - 2^51 - 2^18 + 1 */
#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 Wordsize not 32 or 64
#endif

static __always_inline u64 hash_64(u64 val, unsigned int bits)
{
	u64 hash = val;

#if defined(CONFIG_ARCH_HAS_FAST_MULTIPLIER) && BITS_PER_LONG == 64
	hash = hash * GOLDEN_RATIO_PRIME_64;
#else
	/*  Sigh, gcc can't optimise this alone like it does for 32 bits. */
	u64 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

	/* 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 */
	u32 hash = val * GOLDEN_RATIO_PRIME_32;

	/* High bits are more random, so use them. */
	return hash >> (32 - bits);
}

static inline unsigned long hash_ptr(const void *ptr, unsigned int bits)
{
	return hash_long((unsigned long)ptr, bits);
}

static inline u32 hash32_ptr(const void *ptr)
{
	unsigned long val = (unsigned long)ptr;

#if BITS_PER_LONG == 64
	val ^= (val >> 32);
#endif
	return (u32)val;
}

#endif /* _LINUX_HASH_H */
Commit	Line	Data
1da177e4 LT	1	#ifndef _LINUX_HASH_H
1da177e4 LT	2	#define _LINUX_HASH_H
4e701482	3	/* Fast hashing routine for ints, longs and pointers.
6d49e352	4	(C) 2002 Nadia Yvette Chambers, IBM */
1da177e4 LT	5
	6	/*
	7	* Knuth recommends primes in approximately golden ratio to the maximum
	8	* integer representable by a machine word for multiplicative hashing.
	9	* Chuck Lever verified the effectiveness of this technique:
	10	* http://www.citi.umich.edu/techreports/reports/citi-tr-00-1.pdf
	11	*
	12	* These primes are chosen to be bit-sparse, that is operations on
	13	* them can use shifts and additions instead of multiplications for
	14	* machines where multiplications are slow.
	15	*/
4e701482 MW	16
4e701482 MW	17	#include <asm/types.h>
65c10553	18	#include <linux/compiler.h>
4e701482	19
1da177e4	20	/* 2^31 + 2^29 - 2^25 + 2^22 - 2^19 - 2^16 + 1 */
4e701482	21	#define GOLDEN_RATIO_PRIME_32 0x9e370001UL
1da177e4	22	/* 2^63 + 2^61 - 2^57 + 2^54 - 2^51 - 2^18 + 1 */
4e701482 MW	23	#define GOLDEN_RATIO_PRIME_64 0x9e37fffffffc0001UL
	24
	25	#if BITS_PER_LONG == 32
	26	#define GOLDEN_RATIO_PRIME GOLDEN_RATIO_PRIME_32
	27	#define hash_long(val, bits) hash_32(val, bits)
	28	#elif BITS_PER_LONG == 64
	29	#define hash_long(val, bits) hash_64(val, bits)
	30	#define GOLDEN_RATIO_PRIME GOLDEN_RATIO_PRIME_64
1da177e4	31	#else
4e701482	32	#error Wordsize not 32 or 64
1da177e4 LT	33	#endif
1da177e4 LT	34
65c10553	35	static __always_inline u64 hash_64(u64 val, unsigned int bits)
1da177e4	36	{
4e701482	37	u64 hash = val;
1da177e4	38
23d0db76 LT	39	#if defined(CONFIG_ARCH_HAS_FAST_MULTIPLIER) && BITS_PER_LONG == 64
	40	hash = hash * GOLDEN_RATIO_PRIME_64;
	41	#else
1da177e4	42	/* Sigh, gcc can't optimise this alone like it does for 32 bits. */
4e701482	43	u64 n = hash;
1da177e4 LT	44	n <<= 18;
	45	hash -= n;
	46	n <<= 33;
	47	hash -= n;
	48	n <<= 3;
	49	hash += n;
	50	n <<= 3;
	51	hash -= n;
	52	n <<= 4;
	53	hash += n;
	54	n <<= 2;
	55	hash += n;
23d0db76	56	#endif
4e701482 MW	57
	58	/* High bits are more random, so use them. */
	59	return hash >> (64 - bits);
	60	}
	61
	62	static inline u32 hash_32(u32 val, unsigned int bits)
	63	{
1da177e4	64	/* On some cpus multiply is faster, on others gcc will do shifts */
4e701482	65	u32 hash = val * GOLDEN_RATIO_PRIME_32;
1da177e4 LT	66
1da177e4 LT	67	/* High bits are more random, so use them. */
4e701482	68	return hash >> (32 - bits);
1da177e4	69	}
4e701482	70
f9918794	71	static inline unsigned long hash_ptr(const void *ptr, unsigned int bits)
1da177e4 LT	72	{
	73	return hash_long((unsigned long)ptr, bits);
	74	}
b14f243a PE	75
	76	static inline u32 hash32_ptr(const void *ptr)
	77	{
	78	unsigned long val = (unsigned long)ptr;
	79
	80	#if BITS_PER_LONG == 64
	81	val ^= (val >> 32);
	82	#endif
	83	return (u32)val;
	84	}
71ae8aac	85
1da177e4	86	#endif /* _LINUX_HASH_H */