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Side by Side Diff: net/disk_cache/hash.cc

Issue 10920026: Move hash.h/cc from net/disk_cache to base. (Closed) Base URL: svn://svn.chromium.org/chrome/trunk/src
Patch Set: willchan, rvargas feedback Created 8 years, 3 months ago
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1 // From http://www.azillionmonkeys.com/qed/hash.html
2
3 #include "net/disk_cache/hash.h"
4
5 typedef uint32 uint32_t;
6 typedef uint16 uint16_t;
7
8 namespace 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
21 uint32 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:
43 hash += get16bits(data);
44 hash ^= hash << 16;
45
46 // Treat the final character as signed. This ensures all platforms behave
47 // consistently with the original x86 code.
48 hash ^= static_cast<signed char>(data[sizeof(uint16_t)]) << 18;
49 hash += hash >> 11;
50 break;
51 case 2:
52 hash += get16bits(data);
53 hash ^= hash << 11;
54 hash += hash >> 17;
55 break;
56 case 1:
57 hash += static_cast<signed char>(*data);
58 hash ^= hash << 10;
59 hash += hash >> 1;
60 }
61
62 /* Force "avalanching" of final 127 bits */
63 hash ^= hash << 3;
64 hash += hash >> 5;
65 hash ^= hash << 4;
66 hash += hash >> 17;
67 hash ^= hash << 25;
68 hash += hash >> 6;
69
70 return hash;
71 }
72
73 } // namespace disk_cache
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