74 lines
1.7 KiB
C++
74 lines
1.7 KiB
C++
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// From http://www.azillionmonkeys.com/qed/hash.html
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#include "base/hash.h"
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typedef uint32 uint32_t;
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typedef uint16 uint16_t;
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namespace base {
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#undef get16bits
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#if (defined(__GNUC__) && defined(__i386__)) || defined(__WATCOMC__) \
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|| defined(_MSC_VER) || defined (__BORLANDC__) || defined (__TURBOC__)
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#define get16bits(d) (*((const uint16_t *) (d)))
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#endif
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#if !defined (get16bits)
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#define get16bits(d) ((((uint32_t)(((const uint8_t *)(d))[1])) << 8)\
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+(uint32_t)(((const uint8_t *)(d))[0]) )
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#endif
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uint32 SuperFastHash(const char * data, int len) {
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uint32_t hash = len, tmp;
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int rem;
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if (len <= 0 || data == NULL)
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return 0;
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rem = len & 3;
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len >>= 2;
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/* Main loop */
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for (; len > 0; len--) {
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hash += get16bits(data);
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tmp = (get16bits(data + 2) << 11) ^ hash;
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hash = (hash << 16) ^ tmp;
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data += 2 * sizeof(uint16_t);
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hash += hash >> 11;
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}
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/* Handle end cases */
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switch (rem) {
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case 3:
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hash += get16bits(data);
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hash ^= hash << 16;
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// Treat the final character as signed. This ensures all platforms behave
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// consistently with the original x86 code.
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hash ^= static_cast<signed char>(data[sizeof(uint16_t)]) << 18;
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hash += hash >> 11;
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break;
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case 2:
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hash += get16bits(data);
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hash ^= hash << 11;
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hash += hash >> 17;
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break;
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case 1:
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hash += static_cast<signed char>(*data);
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hash ^= hash << 10;
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hash += hash >> 1;
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}
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/* Force "avalanching" of final 127 bits */
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hash ^= hash << 3;
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hash += hash >> 5;
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hash ^= hash << 4;
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hash += hash >> 17;
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hash ^= hash << 25;
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hash += hash >> 6;
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return hash;
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}
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} // namespace base
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