1: /* jhash.h: Jenkins hash support.
2: *
3: * Copyright (C) 1996 Bob Jenkins (bob_jenkins@burtleburtle.net)
4: *
5: * http://burtleburtle.net/bob/hash/
6: *
7: * These are the credits from Bob's sources:
8: *
9: * lookup2.c, by Bob Jenkins, December 1996, Public Domain.
10: * hash(), hash2(), hash3, and mix() are externally useful functions.
11: * Routines to test the hash are included if SELF_TEST is defined.
12: * You can use this free for any purpose. It has no warranty.
13: *
14: * Copyright (C) 2003 David S. Miller (davem@redhat.com)
15: *
16: * I've modified Bob's hash to be useful in the Linux kernel, and
17: * any bugs present are surely my fault. -DaveM
18: */
19:
20: #include "zebra.h"
21: #include "jhash.h"
22:
23: /* The golden ration: an arbitrary value */
24: #define JHASH_GOLDEN_RATIO 0x9e3779b9
25:
26: /* NOTE: Arguments are modified. */
27: #define __jhash_mix(a, b, c) \
28: { \
29: a -= b; a -= c; a ^= (c>>13); \
30: b -= c; b -= a; b ^= (a<<8); \
31: c -= a; c -= b; c ^= (b>>13); \
32: a -= b; a -= c; a ^= (c>>12); \
33: b -= c; b -= a; b ^= (a<<16); \
34: c -= a; c -= b; c ^= (b>>5); \
35: a -= b; a -= c; a ^= (c>>3); \
36: b -= c; b -= a; b ^= (a<<10); \
37: c -= a; c -= b; c ^= (b>>15); \
38: }
39:
40: /* The most generic version, hashes an arbitrary sequence
41: * of bytes. No alignment or length assumptions are made about
42: * the input key.
43: */
44: u_int32_t
45: jhash (const void *key, u_int32_t length, u_int32_t initval)
46: {
47: u_int32_t a, b, c, len;
48: const u_int8_t *k = key;
49:
50: len = length;
51: a = b = JHASH_GOLDEN_RATIO;
52: c = initval;
53:
54: while (len >= 12)
55: {
56: a +=
57: (k[0] + ((u_int32_t) k[1] << 8) + ((u_int32_t) k[2] << 16) +
58: ((u_int32_t) k[3] << 24));
59: b +=
60: (k[4] + ((u_int32_t) k[5] << 8) + ((u_int32_t) k[6] << 16) +
61: ((u_int32_t) k[7] << 24));
62: c +=
63: (k[8] + ((u_int32_t) k[9] << 8) + ((u_int32_t) k[10] << 16) +
64: ((u_int32_t) k[11] << 24));
65:
66: __jhash_mix (a, b, c);
67:
68: k += 12;
69: len -= 12;
70: }
71:
72: c += length;
73: switch (len)
74: {
75: case 11:
76: c += ((u_int32_t) k[10] << 24);
77: case 10:
78: c += ((u_int32_t) k[9] << 16);
79: case 9:
80: c += ((u_int32_t) k[8] << 8);
81: case 8:
82: b += ((u_int32_t) k[7] << 24);
83: case 7:
84: b += ((u_int32_t) k[6] << 16);
85: case 6:
86: b += ((u_int32_t) k[5] << 8);
87: case 5:
88: b += k[4];
89: case 4:
90: a += ((u_int32_t) k[3] << 24);
91: case 3:
92: a += ((u_int32_t) k[2] << 16);
93: case 2:
94: a += ((u_int32_t) k[1] << 8);
95: case 1:
96: a += k[0];
97: };
98:
99: __jhash_mix (a, b, c);
100:
101: return c;
102: }
103:
104: /* A special optimized version that handles 1 or more of u_int32_ts.
105: * The length parameter here is the number of u_int32_ts in the key.
106: */
107: u_int32_t
108: jhash2 (const u_int32_t *k, u_int32_t length, u_int32_t initval)
109: {
110: u_int32_t a, b, c, len;
111:
112: a = b = JHASH_GOLDEN_RATIO;
113: c = initval;
114: len = length;
115:
116: while (len >= 3)
117: {
118: a += k[0];
119: b += k[1];
120: c += k[2];
121: __jhash_mix (a, b, c);
122: k += 3;
123: len -= 3;
124: }
125:
126: c += length * 4;
127:
128: switch (len)
129: {
130: case 2:
131: b += k[1];
132: case 1:
133: a += k[0];
134: };
135:
136: __jhash_mix (a, b, c);
137:
138: return c;
139: }
140:
141:
142: /* A special ultra-optimized versions that knows they are hashing exactly
143: * 3, 2 or 1 word(s).
144: *
145: * NOTE: In partilar the "c += length; __jhash_mix(a,b,c);" normally
146: * done at the end is not done here.
147: */
148: u_int32_t
149: jhash_3words (u_int32_t a, u_int32_t b, u_int32_t c, u_int32_t initval)
150: {
151: a += JHASH_GOLDEN_RATIO;
152: b += JHASH_GOLDEN_RATIO;
153: c += initval;
154:
155: __jhash_mix (a, b, c);
156:
157: return c;
158: }
159:
160: u_int32_t
161: jhash_2words (u_int32_t a, u_int32_t b, u_int32_t initval)
162: {
163: return jhash_3words (a, b, 0, initval);
164: }
165:
166: u_int32_t
167: jhash_1word (u_int32_t a, u_int32_t initval)
168: {
169: return jhash_3words (a, 0, 0, initval);
170: }
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