memcpy.c

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/*-
 * Copyright (c) 1990, 1993
 *  The Regents of the University of California.  All rights reserved.
 *
 * This code is derived from software contributed to Berkeley by
 * Chris Torek.
 *
 * Redistribution and use in source and binary forms, with or without
 * modification, are permitted provided that the following conditions
 * are met:
 * 1. Redistributions of source code must retain the above copyright
 *    notice, this list of conditions and the following disclaimer.
 * 2. Redistributions in binary form must reproduce the above copyright
 *    notice, this list of conditions and the following disclaimer in the
 *    documentation and/or other materials provided with the distribution.
 * 4. Neither the name of the University nor the names of its contributors
 *    may be used to endorse or promote products derived from this software
 *    without specific prior written permission.
 *
 * THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND
 * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
 * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
 * ARE DISCLAIMED.  IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE
 * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
 * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
 * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
 * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
 * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
 * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
 * SUCH DAMAGE.
 */

#include <string.h>

/*
 * sizeof(word) MUST BE A POWER OF TWO
 * SO THAT wmask BELOW IS ALL ONES
 */
typedef int word; /* "word" used for optimal copy speed */

#define wsize sizeof(word)
#define wmask (wsize - 1)

/*
 * Copy a block of memory, handling overlap.
 * This is the routine that actually implements
 * (the portable versions of) bcopy, memcpy, and memmove.
 */
void* memcpy(void* dst0, const void* src0, size_t length)
{
    char* dst = dst0;
    const char* src = src0;
    size_t t;

    if(length == 0 || dst == src)
    {
        { /* nothing to do */
            goto done;
        }
    }

/*
 * Macros: loop-t-times; and loop-t-times, t>0
 */
// clang-format off
#define TLOOP(s) if (t) TLOOP1(s)
#define TLOOP1(s) do { s; } while (--t)
    // clang-format on

    if((uintptr_t)dst < (uintptr_t)src)
    {
        /*
         * Copy forward.
         */
        t = (uintptr_t)src; /* only need low bits */
        if((t | (uintptr_t)dst) & wmask)
        {
            /*
             * Try to align operands.  This cannot be done
             * unless the low bits match.
             */
            if((t ^ (uintptr_t)dst) & wmask || length < wsize)
            {
                {
                    t = length;
                }
            }
            else
            {
                {
                    t = wsize - (t & wmask);
                }
            }
            length -= t;
            TLOOP1(*dst++ = *src++);
        }
        /*
         * Copy whole words, then mop up any trailing bytes.
         */
        t = length / wsize;
        // Silence warning for alignment change by casting to void*
        TLOOP(*(word*)(void*)dst = *(const word*)(const void*)src; src += wsize; dst += wsize);
        t = length & wmask;
        TLOOP(*dst++ = *src++);
    }
    else
    {
        /*
         * Copy backwards.  Otherwise essentially the same.
         * Alignment works as before, except that it takes
         * (t&wmask) bytes to align, not wsize-(t&wmask).
         */
        src += length;
        dst += length;
        t = (uintptr_t)src;
        if((t | (uintptr_t)dst) & wmask)
        {
            if((t ^ (uintptr_t)dst) & wmask || length <= wsize)
            {
                {
                    t = length;
                }
            }
            else
            {
                {
                    t &= wmask;
                }
            }
            length -= t;
            TLOOP1(*--dst = *--src);
        }
        t = length / wsize;
        // Silence warning for alignment change by casting to void*
        TLOOP(src -= wsize; dst -= wsize; *(word*)(void*)dst = *(const word*)(const void*)src);
        t = length & wmask;
        TLOOP(*--dst = *--src);
    }
done:
    return (dst0);
}