source: vbox/trunk/src/VBox/Runtime/include/internal/strhash.h@ 36597

/* $Id: strhash.h 36597 2011-04-06 19:46:15Z vboxsync $ */
/** @file
 * IPRT - Internal header containing inline string hashing functions.
 */

/*
 * Copyright (C) 2006-2011 Oracle Corporation
 *
 * This file is part of VirtualBox Open Source Edition (OSE), as
 * available from http://www.virtualbox.org. This file is free software;
 * you can redistribute it and/or modify it under the terms of the GNU
 * General Public License (GPL) as published by the Free Software
 * Foundation, in version 2 as it comes in the "COPYING" file of the
 * VirtualBox OSE distribution. VirtualBox OSE is distributed in the
 * hope that it will be useful, but WITHOUT ANY WARRANTY of any kind.
 *
 * The contents of this file may alternatively be used under the terms
 * of the Common Development and Distribution License Version 1.0
 * (CDDL) only, as it comes in the "COPYING.CDDL" file of the
 * VirtualBox OSE distribution, in which case the provisions of the
 * CDDL are applicable instead of those of the GPL.
 *
 * You may elect to license modified versions of this file under the
 * terms and conditions of either the GPL or the CDDL or both.
 */

#ifndef ___internal_strhash_h
#define ___internal_strhash_h

#include <iprt/types.h>


/* sdbm:
   This algorithm was created for sdbm (a public-domain reimplementation of
   ndbm) database library. it was found to do well in scrambling bits,
   causing better distribution of the keys and fewer splits. it also happens
   to be a good general hashing function with good distribution. the actual
   function is hash(i) = hash(i - 1) * 65599 + str[i]; what is included below
   is the faster version used in gawk. [there is even a faster, duff-device
   version] the magic constant 65599 was picked out of thin air while
   experimenting with different constants, and turns out to be a prime.
   this is one of the algorithms used in berkeley db (see sleepycat) and
   elsewhere. */

/**
 * Hash string, return hash + length.
 */
DECLINLINE(uint32_t) sdbm(const char *str, size_t *pcch)
{
    uint8_t *pu8 = (uint8_t *)str;
    uint32_t hash = 0;
    int c;

    while ((c = *pu8++))
        hash = c + (hash << 6) + (hash << 16) - hash;

    *pcch = (uintptr_t)pu8 - (uintptr_t)str - 1;
    return hash;
}


/**
 * Hash up to N bytes, return hash + hashed length.
 */
DECLINLINE(uint32_t) sdbmN(const char *str, size_t cchMax, size_t *pcch)
{
    uint8_t *pu8 = (uint8_t *)str;
    uint32_t hash = 0;
    int c;

    while ((c = *pu8++) && cchMax-- > 0)
        hash = c + (hash << 6) + (hash << 16) - hash;

    *pcch = (uintptr_t)pu8 - (uintptr_t)str - 1;
    return hash;
}

/**
 * Incremental hashing.
 */
DECLINLINE(uint32_t) sdbmInc(const char *str, uint32_t hash)
{
    uint8_t *pu8 = (uint8_t *)str;
    int c;

    while ((c = *pu8++))
        hash = c + (hash << 6) + (hash << 16) - hash;

    return hash;
}


#endif