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
|
/* This file is part of the Spring engine (GPL v2 or later), see LICENSE.html */
#ifndef HSIEH_HASH_H
#define HSIEH_HASH_H
#include <boost/cstdint.hpp> /* Replace with <stdint.h> if appropriate */
#undef get16bits
#if (defined(__GNUC__) && defined(__i386__)) || defined(__WATCOMC__) \
|| defined(_MSC_VER) || defined (__BORLANDC__) || defined (__TURBOC__)
#define get16bits(d) (*((const boost::uint16_t *) (d)))
#endif
#if !defined (get16bits)
#define get16bits(d) ((((boost::uint32_t)(((const boost::uint8_t *)(d))[1])) << 8)\
+(boost::uint32_t)(((const boost::uint8_t *)(d))[0]) )
#endif
/** @brief a fast hash function
*
* This hash function is roughly 4x as fast as CRC32, but even that is too slow.
* We use a very simplistic add/xor feedback scheme when not debugging.
*/
static inline boost::uint32_t HsiehHash (const char * data, int len, boost::uint32_t hash)
{
boost::uint32_t tmp;
int rem;
if (len <= 0 || data == NULL) return 0;
rem = len & 3;
len >>= 2;
/* Main loop */
for (;len > 0; len--) {
hash += get16bits (data);
tmp = (get16bits (data+2) << 11) ^ hash;
hash = (hash << 16) ^ tmp;
data += 2*sizeof (boost::uint16_t);
hash += hash >> 11;
}
/* Handle end cases */
switch (rem) {
case 3:
hash += get16bits (data);
hash ^= hash << 16;
hash ^= data[sizeof (boost::uint16_t)] << 18;
hash += hash >> 11;
break;
case 2:
hash += get16bits (data);
hash ^= hash << 11;
hash += hash >> 17;
break;
case 1:
hash += *data;
hash ^= hash << 10;
hash += hash >> 1;
break;
}
/* Force "avalanching" of final 127 bits */
hash ^= hash << 3;
hash += hash >> 5;
hash ^= hash << 4;
hash += hash >> 17;
hash ^= hash << 25;
hash += hash >> 6;
return hash;
}
#endif // !defined(HSIEH_HASH_H)
|
