summaryrefslogtreecommitdiff
path: root/net/ceph/ceph_hash.c
blob: 81e1e006c5404ddb3d18c78d4bb89850cde198e1 (plain)
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
#include <linux/ceph/types.h>
#include <linux/module.h>

/*
 * Robert Jenkin's hash function.
 * https://burtleburtle.net/bob/hash/evahash.html
 * This is in the public domain.
 */
#define mix(a, b, c)						\
	do {							\
		a = a - b;  a = a - c;  a = a ^ (c >> 13);	\
		b = b - c;  b = b - a;  b = b ^ (a << 8);	\
		c = c - a;  c = c - b;  c = c ^ (b >> 13);	\
		a = a - b;  a = a - c;  a = a ^ (c >> 12);	\
		b = b - c;  b = b - a;  b = b ^ (a << 16);	\
		c = c - a;  c = c - b;  c = c ^ (b >> 5);	\
		a = a - b;  a = a - c;  a = a ^ (c >> 3);	\
		b = b - c;  b = b - a;  b = b ^ (a << 10);	\
		c = c - a;  c = c - b;  c = c ^ (b >> 15);	\
	} while (0)

unsigned int ceph_str_hash_rjenkins(const char *str, unsigned int length)
{
	const unsigned char *k = (const unsigned char *)str;
	__u32 a, b, c;  /* the internal state */
	__u32 len;      /* how many key bytes still need mixing */

	/* Set up the internal state */
	len = length;
	a = 0x9e3779b9;      /* the golden ratio; an arbitrary value */
	b = a;
	c = 0;               /* variable initialization of internal state */

	/* handle most of the key */
	while (len >= 12) {
		a = a + (k[0] + ((__u32)k[1] << 8) + ((__u32)k[2] << 16) +
			 ((__u32)k[3] << 24));
		b = b + (k[4] + ((__u32)k[5] << 8) + ((__u32)k[6] << 16) +
			 ((__u32)k[7] << 24));
		c = c + (k[8] + ((__u32)k[9] << 8) + ((__u32)k[10] << 16) +
			 ((__u32)k[11] << 24));
		mix(a, b, c);
		k = k + 12;
		len = len - 12;
	}

	/* handle the last 11 bytes */
	c = c + length;
	switch (len) {
	case 11:
		c = c + ((__u32)k[10] << 24);
		/* fall through */
	case 10:
		c = c + ((__u32)k[9] << 16);
		/* fall through */
	case 9:
		c = c + ((__u32)k[8] << 8);
		/* the first byte of c is reserved for the length */
		/* fall through */
	case 8:
		b = b + ((__u32)k[7] << 24);
		/* fall through */
	case 7:
		b = b + ((__u32)k[6] << 16);
		/* fall through */
	case 6:
		b = b + ((__u32)k[5] << 8);
		/* fall through */
	case 5:
		b = b + k[4];
		/* fall through */
	case 4:
		a = a + ((__u32)k[3] << 24);
		/* fall through */
	case 3:
		a = a + ((__u32)k[2] << 16);
		/* fall through */
	case 2:
		a = a + ((__u32)k[1] << 8);
		/* fall through */
	case 1:
		a = a + k[0];
		/* case 0: nothing left to add */
	}
	mix(a, b, c);

	return c;
}

/*
 * linux dcache hash
 */
unsigned int ceph_str_hash_linux(const char *str, unsigned int length)
{
	unsigned long hash = 0;
	unsigned char c;

	while (length--) {
		c = *str++;
		hash = (hash + (c << 4) + (c >> 4)) * 11;
	}
	return hash;
}


unsigned int ceph_str_hash(int type, const char *s, unsigned int len)
{
	switch (type) {
	case CEPH_STR_HASH_LINUX:
		return ceph_str_hash_linux(s, len);
	case CEPH_STR_HASH_RJENKINS:
		return ceph_str_hash_rjenkins(s, len);
	default:
		return -1;
	}
}
EXPORT_SYMBOL(ceph_str_hash);

const char *ceph_str_hash_name(int type)
{
	switch (type) {
	case CEPH_STR_HASH_LINUX:
		return "linux";
	case CEPH_STR_HASH_RJENKINS:
		return "rjenkins";
	default:
		return "unknown";
	}
}
EXPORT_SYMBOL(ceph_str_hash_name);