1#ifndef _LINUX_HASH_H
2#define _LINUX_HASH_H
3/* Fast hashing routine for ints,  longs and pointers.
4   (C) 2002 William Lee Irwin III, IBM */
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 */
16
17/* ANDROID_CHANGE_BEGIN */
18#ifndef __APPLE__
19#include <asm/types.h>
20#endif
21/* ANDROID_CHANGE_END */
22
23/* 2^31 + 2^29 - 2^25 + 2^22 - 2^19 - 2^16 + 1 */
24#define GOLDEN_RATIO_PRIME_32 0x9e370001UL
25/*  2^63 + 2^61 - 2^57 + 2^54 - 2^51 - 2^18 + 1 */
26#define GOLDEN_RATIO_PRIME_64 0x9e37fffffffc0001UL
27
28#if BITS_PER_LONG == 32
29#define GOLDEN_RATIO_PRIME GOLDEN_RATIO_PRIME_32
30#define hash_long(val, bits) hash_32(val, bits)
31#elif BITS_PER_LONG == 64
32#define hash_long(val, bits) hash_64(val, bits)
33#define GOLDEN_RATIO_PRIME GOLDEN_RATIO_PRIME_64
34#else
35#error Wordsize not 32 or 64
36#endif
37
38static inline u64 hash_64(u64 val, unsigned int bits)
39{
40	u64 hash = val;
41
42	/*  Sigh, gcc can't optimise this alone like it does for 32 bits. */
43	u64 n = hash;
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;
56
57	/* High bits are more random, so use them. */
58	return hash >> (64 - bits);
59}
60
61static inline u32 hash_32(u32 val, unsigned int bits)
62{
63	/* On some cpus multiply is faster, on others gcc will do shifts */
64	u32 hash = val * GOLDEN_RATIO_PRIME_32;
65
66	/* High bits are more random, so use them. */
67	return hash >> (32 - bits);
68}
69
70static inline unsigned long hash_ptr(void *ptr, unsigned int bits)
71{
72	return hash_long((unsigned long)ptr, bits);
73}
74#endif /* _LINUX_HASH_H */
75