blob: 66187912fca5c360e889e1e584366e4f3d6b5f70 [file] [log] [blame]
// Copyright (c) 2010, Paul Hsieh
// All rights reserved.
//
// Redistribution and use in source and binary forms, with or without
// modification, are permitted provided that the following conditions are met:
//
// * Redistributions of source code must retain the above copyright notice, this
// list of conditions and the following disclaimer.
// * Redistributions in binary form must reproduce the above copyright notice,
// this list of conditions and the following disclaimer in the documentation
// and/or other materials provided with the distribution.
// * Neither my name, Paul Hsieh, nor the names of any other contributors to the
// code use may not be used to endorse or promote products derived from this
// software without specific prior written permission.
//
// THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS"
// AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
// IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
// ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT OWNER OR CONTRIBUTORS BE
// LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR
// CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF
// SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS
// INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN
// CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE)
// ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE
// POSSIBILITY OF SUCH DAMAGE.
// From http://www.azillionmonkeys.com/qed/hash.html
#if SB_IS(BIG_ENDIAN)
#define get16bits(d) (*((const uint16_t *) (d)))
#else
#define get16bits(d) ((((uint32_t)(((const uint8_t *)(d))[1])) << 8)\
+(uint32_t)(((const uint8_t *)(d))[0]) )
#endif
uint32_t SuperFastHash(const char* data, int len, uint32_t prev_hash) {
uint32_t hash = prev_hash, 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;
}