69 lines
1.8 KiB
C++
69 lines
1.8 KiB
C++
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// File: crn_hash.cpp
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// See Paul Hsieh's page at: http://www.azillionmonkeys.com/qed/hash.html
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// Also see http://www.concentric.net/~Ttwang/tech/inthash.htm,
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// http://burtleburtle.net/bob/hash/integer.html
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#include "crn_core.h"
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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 *) (d)))
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#endif
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#if !defined (get16bits)
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#define get16bits(d) ((((uint32)(((const uint8 *)(d))[1])) << 8)\
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+(uint32)(((const uint8 *)(d))[0]) )
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#endif
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namespace crnlib
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{
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uint32 fast_hash (const void* p, int len)
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{
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const char * data = static_cast<const char *>(p);
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uint32 hash = len, tmp;
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int rem;
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if (len <= 0 || data == NULL) 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);
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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: hash += get16bits (data);
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hash ^= hash << 16;
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hash ^= data[sizeof (uint16)] << 18;
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hash += hash >> 11;
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break;
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case 2: 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: hash += *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 crnlib
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