FreeBSD/Linux Kernel Cross Reference
sys/libkern/bcopy.c

     /*-
      * SPDX-License-Identifier: BSD-3-Clause
      * Copyright (c) 1990 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.
     * 3. 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.
     */
    
    #if defined(LIBC_SCCS) && !defined(lint)
    #if 0
    static char *sccsid = "from: @(#)bcopy.c      5.11 (Berkeley) 6/21/91";
    #endif
    #if 0
    static char *rcsid = "$NetBSD: bcopy.c,v 1.2 1997/04/16 22:09:41 thorpej Exp $";
    #endif
    #endif /* LIBC_SCCS and not lint */
    #include <sys/cdefs.h>
    __FBSDID("$FreeBSD$");
    
    #include <sys/param.h>
    #ifdef _KERNEL
    #include <sys/systm.h>
    #else
    #include <string.h>
    #endif
    
    #undef memcpy
    #undef memmove
    
    /*
     * sizeof(word) MUST BE A POWER OF TWO
     * SO THAT wmask BELOW IS ALL ONES
     */
    typedef long    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;
            const char      *src;
            size_t          t;
    
            dst = dst0;
            src = src0;
    
            if (length == 0 || dst == src) {        /* nothing to do */
                    goto done;
            }
    
            /*
             * Macros: loop-t-times; and loop-t-times, t>0
             */
    #define TLOOP(s) if (t) TLOOP1(s)
    #define TLOOP1(s) do { s; } while (--t)
    
            if ((unsigned long)dst < (unsigned long)src) {
                    /*
                     * Copy forward.
                     */
                    t = (size_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;
                   TLOOP(*(word *)dst = *(const word *)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;
                   TLOOP(src -= wsize; dst -= wsize;
                       *(word *)dst = *(const word *)src);
                   t = length & wmask;
                   TLOOP(*--dst = *--src);
           }
   done:
           return (dst0);
   }
   
   __strong_reference(memcpy, memmove);

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