fnv_hash.cpp

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/* Copyright (c) 2010 Wildfire Games
 *
 * Permission is hereby granted, free of charge, to any person obtaining
 * a copy of this software and associated documentation files (the
 * "Software"), to deal in the Software without restriction, including
 * without limitation the rights to use, copy, modify, merge, publish,
 * distribute, sublicense, and/or sell copies of the Software, and to
 * permit persons to whom the Software is furnished to do so, subject to
 * the following conditions:
 * 
 * The above copyright notice and this permission notice shall be included
 * in all copies or substantial portions of the Software.
 * 
 * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND,
 * EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF
 * MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT.
 * IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY
 * CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN ACTION OF CONTRACT,
 * TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION WITH THE
 * SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.
 */

/*
 * Fowler/Noll/Vo string hash
 */

#include "precompiled.h"


// FNV1-A hash - good for strings.
// if len = 0 (default), treat buf as a C-string;
// otherwise, hash <len> bytes of buf.
u32 fnv_hash(const void* buf, size_t len)
{
    u32 h = 0x811c9dc5u;
    // give distinct values for different length 0 buffers.
    // value taken from FNV; it has no special significance.

    const u8* p = (const u8*)buf;

    // expected case: string
    if(!len)
    {
        while(*p)
        {
            h ^= *p++;
            h *= 0x01000193u;
        }
    }
    else
    {
        size_t bytes_left = len;
        while(bytes_left != 0)
        {
            h ^= *p++;
            h *= 0x01000193u;

            bytes_left--;
        }
    }

    return h;
}


// FNV1-A hash - good for strings.
// if len = 0 (default), treat buf as a C-string;
// otherwise, hash <len> bytes of buf.
u64 fnv_hash64(const void* buf, size_t len)
{
    u64 h = 0xCBF29CE484222325ull;
    // give distinct values for different length 0 buffers.
    // value taken from FNV; it has no special significance.

    const u8* p = (const u8*)buf;

    // expected case: string
    if(!len)
    {
        while(*p)
        {
            h ^= *p++;
            h *= 0x100000001B3ull;
        }
    }
    else
    {
        size_t bytes_left = len;
        while(bytes_left != 0)
        {
            h ^= *p++;
            h *= 0x100000001B3ull;

            bytes_left--;
        }
    }

    return h;
}


// special version for strings: first converts to lowercase
// (useful for comparing mixed-case filenames).
// note: still need <len>, e.g. to support non-0-terminated strings
u32 fnv_lc_hash(const char* str, size_t len)
{
    u32 h = 0x811c9dc5u;
    // give distinct values for different length 0 buffers.
    // value taken from FNV; it has no special significance.

    // expected case: string
    if(!len)
    {
        while(*str)
        {
            h ^= tolower(*str++);
            h *= 0x01000193u;
        }
    }
    else
    {
        size_t bytes_left = len;
        while(bytes_left != 0)
        {
            h ^= tolower(*str++);
            h *= 0x01000193u;

            bytes_left--;
        }
    }

    return h;
}