/* $Id: memcmp.cpp $ */
/** @file
 * IPRT - CRT Strings, memcmp().
 */

/*
 * Copyright (C) 2006-2023 Oracle and/or its affiliates.
 *
 * This file is part of VirtualBox base platform packages, as
 * available from https://www.virtualbox.org.
 *
 * This program is free software; you can redistribute it and/or
 * modify it under the terms of the GNU General Public License
 * as published by the Free Software Foundation, in version 3 of the
 * License.
 *
 * This program is distributed in the hope that it will be useful, but
 * WITHOUT ANY WARRANTY; without even the implied warranty of
 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
 * General Public License for more details.
 *
 * You should have received a copy of the GNU General Public License
 * along with this program; if not, see <https://www.gnu.org/licenses>.
 *
 * The contents of this file may alternatively be used under the terms
 * of the Common Development and Distribution License Version 1.0
 * (CDDL), a copy of it is provided in the "COPYING.CDDL" file included
 * in the VirtualBox 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.
 *
 * SPDX-License-Identifier: GPL-3.0-only OR CDDL-1.0
 */


/*********************************************************************************************************************************
*   Header Files                                                                                                                 *
*********************************************************************************************************************************/
#include "internal/iprt.h"
#include <iprt/string.h>


/**
 * Copies a memory.
 *
 * @returns 0 if pvDst and pvSrc are equal
 * @returns <0 if pvDst is 'smaller' than pvSrc.
 * @returns >0 if pvDst is 'larger' than pvSrc.
 *
 * @param   pvDst       Pointer to the target block.
 * @param   pvSrc       Pointer to the source block.
 * @param   cb          The size of the block.
 */
#ifdef IPRT_NO_CRT
# undef memcmp
int RT_NOCRT(memcmp)(const void *pvDst, const void *pvSrc, size_t cb)
#elif RT_MSC_PREREQ(RT_MSC_VER_VS2005)
__checkReturn int __cdecl
memcmp(__in_bcount_opt(_Size) const void *pvDst, __in_bcount_opt(_Size) const void *pvSrc, __in size_t cb)
#else
int memcmp(const void *pvDst, const void *pvSrc, size_t cb)
#endif
{
    union
    {
        uint8_t const  *pu8;
        uint32_t const *pu32;
        void const     *pv;
    } uDst, uSrc;
    uDst.pv = pvDst;
    uSrc.pv = pvSrc;

    /* 32-bit word compare. */
    size_t c = cb >> 2;
    while (c-- > 0)
    {
        /* ASSUMES int is at least 32-bit! */
        int32_t iDiff = *uDst.pu32++ - *uSrc.pu32++;
        if (iDiff)
            return iDiff;
    }

    /* Remaining byte moves. */
    c = cb & 3;
    while (c-- > 0)
    {
        int8_t iDiff = *uDst.pu8++ - *uSrc.pu8++;
        if (iDiff)
            return iDiff;
    }

    return 0;
}
RT_ALIAS_AND_EXPORT_NOCRT_SYMBOL(memcmp);