1/*
2 * Copyright (c) 2005 Voltaire Inc.  All rights reserved.
3 *
4 * This software is available to you under a choice of one of two
5 * licenses.  You may choose to be licensed under the terms of the GNU
6 * General Public License (GPL) Version 2, available from the file
7 * COPYING in the main directory of this source tree, or the
8 * OpenIB.org BSD license below:
9 *
10 *     Redistribution and use in source and binary forms, with or
11 *     without modification, are permitted provided that the following
12 *     conditions are met:
13 *
14 *      - Redistributions of source code must retain the above
15 *        copyright notice, this list of conditions and the following
16 *        disclaimer.
17 *
18 *      - Redistributions in binary form must reproduce the above
19 *        copyright notice, this list of conditions and the following
20 *        disclaimer in the documentation and/or other materials
21 *        provided with the distribution.
22 *
23 * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND,
24 * EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF
25 * MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND
26 * NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS
27 * BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN
28 * ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN
29 * CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
30 * SOFTWARE.
31 *
32 */
33
34/*
35 * By Bob Jenkins, 1996.  bob_jenkins@burtleburtle.net.  You may use this
36 * code any way you wish, private, educational, or commercial.  It's free.
37 *
38 * See http://burtleburtle.net/bob/hash/evahash.html
39 * Use for hash table lookup, or anything where one collision in 2^^32 is
40 * acceptable.  Do NOT use for cryptographic purposes.
41 */
42
43#include <common.h>
44
45#define hashsize(n) ((uint32)1<<(n))
46#define hashmask(n) (hashsize(n)-1)
47
48
49/*
50--------------------------------------------------------------------
51mix -- mix 3 32-bit values reversibly.
52For every delta with one or two bits set, and the deltas of all three
53  high bits or all three low bits, whether the original value of a,b,c
54  is almost all zero or is uniformly distributed,
55* If mix() is run forward or backward, at least 32 bits in a,b,c
56  have at least 1/4 probability of changing.
57* If mix() is run forward, every bit of c will change between 1/3 and
58  2/3 of the time.  (Well, 22/100 and 78/100 for some 2-bit deltas.)
59mix() was built out of 36 single-cycle latency instructions in a
60  structure that could supported 2x parallelism, like so:
61      a -= b;
62      a -= c; x = (c>>13);
63      b -= c; a ^= x;
64      b -= a; x = (a<<8);
65      c -= a; b ^= x;
66      c -= b; x = (b>>13);
67      ...
68  Unfortunately, superscalar Pentiums and Sparcs can't take advantage
69  of that parallelism.  They've also turned some of those single-cycle
70  latency instructions into multi-cycle latency instructions.  Still,
71  this is the fastest good hash I could find.  There were about 2^^68
72  to choose from.  I only looked at a billion or so.
73--------------------------------------------------------------------
74*/
75#define mix(a,b,c) \
76{ \
77	a -= b; a -= c; a ^= (c>>13);	\
78	b -= c; b -= a; b ^= (a<<8);	\
79	c -= a; c -= b; c ^= (b>>13);	\
80	a -= b; a -= c; a ^= (c>>12);	\
81	b -= c; b -= a; b ^= (a<<16);	\
82	c -= a; c -= b; c ^= (b>>5);	\
83	a -= b; a -= c; a ^= (c>>3);	\
84	b -= c; b -= a; b ^= (a<<10);	\
85	c -= a; c -= b; c ^= (b>>15);	\
86}
87
88/*
89--------------------------------------------------------------------
90fhash() -- hash a variable-length key into a 32-bit value
91  k       : the key (the unaligned variable-length array of bytes)
92  len     : the length of the key, counting by bytes
93  initval : can be any 4-byte value
94Returns a 32-bit value.  Every bit of the key affects every bit of
95the return value.  Every 1-bit and 2-bit delta achieves avalanche.
96About 6*len+35 instructions.
97
98The best hash table sizes are powers of 2.  There is no need to do
99mod a prime (mod is sooo slow!).  If you need less than 32 bits,
100use a bitmask.  For example, if you need only 10 bits, do
101  h = (h & hashmask(10));
102In which case, the hash table should have hashsize(10) elements.
103
104If you are hashing n strings (uint8 **)k, do it like this:
105  for (i=0, h=0; i<n; ++i) h = hash( k[i], len[i], h);
106
107--------------------------------------------------------------------
108*/
109
110uint32_t
111fhash(uint8_t *k, int length, uint32_t initval)
112{
113	uint32_t a, b, c, len;
114
115	/* Set up the internal state */
116	len = length;
117	a = b = 0x9e3779b9;		/* the golden ratio; an arbitrary value */
118	c = initval;			/* the previous hash value */
119
120	/* handle most of the key */
121	while (len >= 12) {
122		a += (k[0] + ((uint32_t)k[1]<<8) +
123		      ((uint32_t)k[2]<<16) + ((uint32_t)k[3]<<24));
124		b += (k[4] + ((uint32_t)k[5]<<8) + ((uint32_t)k[6]<<16) +
125		      ((uint32_t)k[7]<<24));
126		c += (k[8] + ((uint32_t)k[9]<<8) + ((uint32_t)k[10]<<16) +
127		      ((uint32_t)k[11]<<24));
128		mix(a, b, c);
129		k += 12; len -= 12;
130	}
131
132	/* handle the last 11 bytes */
133	c += length;
134	switch (len) {		/* all the case statements fall through */
135	case 11: c += ((uint32_t)k[10]<<24);
136	case 10: c += ((uint32_t)k[9]<<16);
137	case 9 : c += ((uint32_t)k[8]<<8);
138		/* the first byte of c is reserved for the length */
139	case 8 : b += ((uint32_t)k[7]<<24);
140	case 7 : b += ((uint32_t)k[6]<<16);
141	case 6 : b += ((uint32_t)k[5]<<8);
142	case 5 : b += k[4];
143	case 4 : a += ((uint32_t)k[3]<<24);
144	case 3 : a += ((uint32_t)k[2]<<16);
145	case 2 : a += ((uint32_t)k[1]<<8);
146	case 1 : a += k[0];
147	  /* case 0: nothing left to add */
148	}
149
150	mix(a, b, c);
151
152	return c;
153}
154