superfasthash.c - mozsearch

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// 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.

#include <stdint.h>

#include <stdlib.h>

#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_t 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;

                hash ^= ((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 += (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;