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Linus Torvalds1da177e2005-04-16 15:20:36 -07001#ifndef _LINUX_HASH_H
2#define _LINUX_HASH_H
Matthew Wilcox4e701482008-02-06 01:36:14 -08003/* Fast hashing routine for ints, longs and pointers.
Nadia Yvette Chambers6d49e352012-12-06 10:39:54 +01004 (C) 2002 Nadia Yvette Chambers, IBM */
Linus Torvalds1da177e2005-04-16 15:20:36 -07005
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 */
Matthew Wilcox4e701482008-02-06 01:36:14 -080016
17#include <asm/types.h>
Masami Hiramatsu65c10552013-03-14 20:52:30 +090018#include <linux/compiler.h>
Matthew Wilcox4e701482008-02-06 01:36:14 -080019
Linus Torvalds1da177e2005-04-16 15:20:36 -070020/* 2^31 + 2^29 - 2^25 + 2^22 - 2^19 - 2^16 + 1 */
Matthew Wilcox4e701482008-02-06 01:36:14 -080021#define GOLDEN_RATIO_PRIME_32 0x9e370001UL
Linus Torvalds1da177e2005-04-16 15:20:36 -070022/* 2^63 + 2^61 - 2^57 + 2^54 - 2^51 - 2^18 + 1 */
Matthew Wilcox4e701482008-02-06 01:36:14 -080023#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
Linus Torvalds1da177e2005-04-16 15:20:36 -070031#else
Matthew Wilcox4e701482008-02-06 01:36:14 -080032#error Wordsize not 32 or 64
Linus Torvalds1da177e2005-04-16 15:20:36 -070033#endif
34
Masami Hiramatsu65c10552013-03-14 20:52:30 +090035static __always_inline u64 hash_64(u64 val, unsigned int bits)
Linus Torvalds1da177e2005-04-16 15:20:36 -070036{
Matthew Wilcox4e701482008-02-06 01:36:14 -080037 u64 hash = val;
Linus Torvalds1da177e2005-04-16 15:20:36 -070038
Linus Torvalds1da177e2005-04-16 15:20:36 -070039 /* Sigh, gcc can't optimise this alone like it does for 32 bits. */
Matthew Wilcox4e701482008-02-06 01:36:14 -080040 u64 n = hash;
Linus Torvalds1da177e2005-04-16 15:20:36 -070041 n <<= 18;
42 hash -= n;
43 n <<= 33;
44 hash -= n;
45 n <<= 3;
46 hash += n;
47 n <<= 3;
48 hash -= n;
49 n <<= 4;
50 hash += n;
51 n <<= 2;
52 hash += n;
Linus Torvalds1da177e2005-04-16 15:20:36 -070053
54 /* High bits are more random, so use them. */
Matthew Wilcox4e701482008-02-06 01:36:14 -080055 return hash >> (64 - bits);
Linus Torvalds1da177e2005-04-16 15:20:36 -070056}
Matthew Wilcox4e701482008-02-06 01:36:14 -080057
58static inline u32 hash_32(u32 val, unsigned int bits)
59{
60 /* On some cpus multiply is faster, on others gcc will do shifts */
61 u32 hash = val * GOLDEN_RATIO_PRIME_32;
62
63 /* High bits are more random, so use them. */
64 return hash >> (32 - bits);
65}
66
Ian Campbellf9918792011-08-17 13:45:09 +010067static inline unsigned long hash_ptr(const void *ptr, unsigned int bits)
Linus Torvalds1da177e2005-04-16 15:20:36 -070068{
69 return hash_long((unsigned long)ptr, bits);
70}
Pavel Emelyanovb14f2432012-08-08 21:52:28 +000071
72static inline u32 hash32_ptr(const void *ptr)
73{
74 unsigned long val = (unsigned long)ptr;
75
76#if BITS_PER_LONG == 64
77 val ^= (val >> 32);
78#endif
79 return (u32)val;
80}
Linus Torvalds1da177e2005-04-16 15:20:36 -070081#endif /* _LINUX_HASH_H */