arena_hash.h

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/*
 * This file is part of LibCSS
 * Licensed under the MIT License,
 *                http://www.opensource.org/licenses/mit-license.php
 *
 * Copyright 2015 Michael Drake <tlsa@netsurf-browser.org>
 */
 
#ifndef css_select_arena_hash_h_
#define css_select_arena_hash_h_
 
#include <stdint.h>
 
static inline uint32_t css__arena_hash(const uint8_t *data, size_t len)
{
        /* Hashing constants */
        const uint32_t m = 0x5bd1e995;
        const int r = 24;
 
        /* Start with length */
        uint32_t h = len;
 
        /* Hash four bytes at a time */
        while (len >= 4) {
                /* If we could ensure 4-byte alignment of the input, this
                 * could be faster. */
                uint32_t k =
                                (((uint32_t) data[0])      ) |
                                (((uint32_t) data[1]) <<  8) |
                                (((uint32_t) data[2]) << 16) |
                                (((uint32_t) data[3]) << 24);
 
                k *= m;
                k ^= k >> r;
                k *= m;
                h *= m;
                h ^= k;
                data += 4;
                len -= 4;
        }
 
        /* Hash any left over bytes */
        switch (len) {
        case 3: h ^= data[2] << 16; /* Fall through */
        case 2: h ^= data[1] << 8;  /* Fall through */
        case 1: h ^= data[0];
                h *= m;
        }
 
        /* Finalise */
        h ^= h >> 13;
        h *= m;
        h ^= h >> 15;
 
        return h;
}
 
#endif