1
2#include "types.h"
3
4/*
5 * Robert Jenkin's hash function.
6 * http://burtleburtle.net/bob/hash/evahash.html
7 * This is in the public domain.
8 */
9#define mix(a, b, c)						\
10	do {							\
11		a = a - b;  a = a - c;  a = a ^ (c >> 13);	\
12		b = b - c;  b = b - a;  b = b ^ (a << 8);	\
13		c = c - a;  c = c - b;  c = c ^ (b >> 13);	\
14		a = a - b;  a = a - c;  a = a ^ (c >> 12);	\
15		b = b - c;  b = b - a;  b = b ^ (a << 16);	\
16		c = c - a;  c = c - b;  c = c ^ (b >> 5);	\
17		a = a - b;  a = a - c;  a = a ^ (c >> 3);	\
18		b = b - c;  b = b - a;  b = b ^ (a << 10);	\
19		c = c - a;  c = c - b;  c = c ^ (b >> 15);	\
20	} while (0)
21
22unsigned ceph_str_hash_rjenkins(const char *str, unsigned length)
23{
24	const unsigned char *k = (const unsigned char *)str;
25	__u32 a, b, c;  /* the internal state */
26	__u32 len;      /* how many key bytes still need mixing */
27
28	/* Set up the internal state */
29	len = length;
30	a = 0x9e3779b9;      /* the golden ratio; an arbitrary value */
31	b = a;
32	c = 0;               /* variable initialization of internal state */
33
34	/* handle most of the key */
35	while (len >= 12) {
36		a = a + (k[0] + ((__u32)k[1] << 8) + ((__u32)k[2] << 16) +
37			 ((__u32)k[3] << 24));
38		b = b + (k[4] + ((__u32)k[5] << 8) + ((__u32)k[6] << 16) +
39			 ((__u32)k[7] << 24));
40		c = c + (k[8] + ((__u32)k[9] << 8) + ((__u32)k[10] << 16) +
41			 ((__u32)k[11] << 24));
42		mix(a, b, c);
43		k = k + 12;
44		len = len - 12;
45	}
46
47	/* handle the last 11 bytes */
48	c = c + length;
49	switch (len) {            /* all the case statements fall through */
50	case 11:
51		c = c + ((__u32)k[10] << 24);
52	case 10:
53		c = c + ((__u32)k[9] << 16);
54	case 9:
55		c = c + ((__u32)k[8] << 8);
56		/* the first byte of c is reserved for the length */
57	case 8:
58		b = b + ((__u32)k[7] << 24);
59	case 7:
60		b = b + ((__u32)k[6] << 16);
61	case 6:
62		b = b + ((__u32)k[5] << 8);
63	case 5:
64		b = b + k[4];
65	case 4:
66		a = a + ((__u32)k[3] << 24);
67	case 3:
68		a = a + ((__u32)k[2] << 16);
69	case 2:
70		a = a + ((__u32)k[1] << 8);
71	case 1:
72		a = a + k[0];
73		/* case 0: nothing left to add */
74	}
75	mix(a, b, c);
76
77	return c;
78}
79
80/*
81 * linux dcache hash
82 */
83unsigned ceph_str_hash_linux(const char *str, unsigned length)
84{
85	unsigned long hash = 0;
86	unsigned char c;
87
88	while (length--) {
89		c = *str++;
90		hash = (hash + (c << 4) + (c >> 4)) * 11;
91	}
92	return hash;
93}
94
95
96unsigned ceph_str_hash(int type, const char *s, unsigned len)
97{
98	switch (type) {
99	case CEPH_STR_HASH_LINUX:
100		return ceph_str_hash_linux(s, len);
101	case CEPH_STR_HASH_RJENKINS:
102		return ceph_str_hash_rjenkins(s, len);
103	default:
104		return -1;
105	}
106}
107
108const char *ceph_str_hash_name(int type)
109{
110	switch (type) {
111	case CEPH_STR_HASH_LINUX:
112		return "linux";
113	case CEPH_STR_HASH_RJENKINS:
114		return "rjenkins";
115	default:
116		return "unknown";
117	}
118}
119