blob: 78634b6233321965d617dd62f4251490a90e6da4 [file] [log] [blame]
// From http://www.azillionmonkeys.com/qed/hash.html
#include "net/disk_cache/hash.h"
typedef uint32 uint32_t;
typedef uint16 uint16_t;
namespace disk_cache {
#undef get16bits
#if (defined(__GNUC__) && defined(__i386__)) || defined(__WATCOMC__) \
|| defined(_MSC_VER) || defined (__BORLANDC__) || defined (__TURBOC__)
#define get16bits(d) (*((const uint16_t *) (d)))
#endif
#if !defined (get16bits)
#define get16bits(d) ((((uint32_t)(((const uint8_t *)(d))[1])) << 8)\
+(uint32_t)(((const uint8_t *)(d))[0]) )
#endif
uint32 SuperFastHash(const char * data, int len) {
uint32_t hash = len, 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(uint16_t);
hash += hash >> 11;
}
/* Handle end cases */
switch (rem) {
case 3:
hash += get16bits(data);
hash ^= hash << 16;
// Treat the final character as signed. This ensures all platforms behave
// consistently with the original x86 code.
hash ^= static_cast<signed char>(data[sizeof(uint16_t)]) << 18;
hash += hash >> 11;
break;
case 2:
hash += get16bits(data);
hash ^= hash << 11;
hash += hash >> 17;
break;
case 1:
hash += static_cast<signed char>(*data);
hash ^= hash << 10;
hash += hash >> 1;
}
/* 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;
}
} // namespace disk_cache