84 lines
2.4 KiB
C++
84 lines
2.4 KiB
C++
/**
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Initial Publish Date: Thu, 16 Oct 2008
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Initial Author: Paul Hsieh
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@file SuperFastHash.c
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@version $Revision$
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@date $LastChangedDate$
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@author $LastChangeAuthor$
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@author Paul Hsieh
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The code below appears to be the fastest hashing algorithm available and is licensed for
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anyone to use. An article describing the has function can be found on the link below. This
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function is used by Safari and some other big-name programs (so it must be good right?)
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http://www.azillionmonkeys.com/qed/hash.html
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*/
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#include <fc/string.hpp>
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#include <fc/super_fast_hash.hpp>
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namespace fc {
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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_t super_fast_hash (const fc::string& str ) {
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return super_fast_hash( str.c_str(), str.size() );
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}
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uint32_t super_fast_hash (const char * data, int len)
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{
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uint32_t hash = len, tmp;
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int rem;
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if (len <= 0 || data == 0) 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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{
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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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{
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case 3: hash += get16bits (data);
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hash ^= hash << 16;
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hash ^= data[sizeof (uint16_t)] << 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 fc
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