arena_hash.h

Go to the documentation of this file.

/*
 * 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