1// From http://www.azillionmonkeys.com/qed/hash.html
2
3#include "net/disk_cache/hash.h"
4
5typedef uint32 uint32_t;
6typedef uint16 uint16_t;
7
8namespace disk_cache {
9
10#undef get16bits
11#if (defined(__GNUC__) && defined(__i386__)) || defined(__WATCOMC__) \
12  || defined(_MSC_VER) || defined (__BORLANDC__) || defined (__TURBOC__)
13#define get16bits(d) (*((const uint16_t *) (d)))
14#endif
15
16#if !defined (get16bits)
17#define get16bits(d) ((((uint32_t)(((const uint8_t *)(d))[1])) << 8)\
18                       +(uint32_t)(((const uint8_t *)(d))[0]) )
19#endif
20
21uint32 SuperFastHash(const char * data, int len) {
22  uint32_t hash = len, tmp;
23  int rem;
24
25  if (len <= 0 || data == NULL)
26    return 0;
27
28  rem = len & 3;
29  len >>= 2;
30
31  /* Main loop */
32  for (;len > 0; len--) {
33    hash  += get16bits(data);
34    tmp    = (get16bits(data + 2) << 11) ^ hash;
35    hash   = (hash << 16) ^ tmp;
36    data  += 2 * sizeof(uint16_t);
37    hash  += hash >> 11;
38  }
39
40  /* Handle end cases */
41  switch (rem) {
42    case 3: hash += get16bits(data);
43      hash ^= hash << 16;
44      hash ^= data[sizeof(uint16_t)] << 18;
45      hash += hash >> 11;
46      break;
47    case 2: hash += get16bits(data);
48      hash ^= hash << 11;
49      hash += hash >> 17;
50      break;
51    case 1: hash += *data;
52      hash ^= hash << 10;
53      hash += hash >> 1;
54  }
55
56  /* Force "avalanching" of final 127 bits */
57  hash ^= hash << 3;
58  hash += hash >> 5;
59  hash ^= hash << 4;
60  hash += hash >> 17;
61  hash ^= hash << 25;
62  hash += hash >> 6;
63
64  return hash;
65}
66
67}  // namespace disk_cache
68