date and time created 91/04/12 13:40:37 by bostic

[unix-history] / usr / src / lib / libc / string / bcopy.c

/*-
* 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.
*
* %sccs.include.redist.c%
*/

#if defined(LIBC_SCCS) && !defined(lint)
static char sccsid[] = "@(#)bcopy.c     5.10 (Berkeley) %G%";
#endif /* LIBC_SCCS and not lint */

#include <sys/cdefs.h>
#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.
*/
#ifdef MEMCOPY
void *
memcpy(dst0, src0, length)
#else
#ifdef MEMMOVE
void *
memmove(dst0, src0, length)
#else
void
bcopy(src0, dst0, length)
#endif
#endif
       void *dst0;
       const void *src0;
       register size_t length;
{
       register char *dst = dst0;
       register const char *src = src0;
       register size_t t;

       if (length == 0 || dst == src)          /* nothing to do */
               return;

       /*
        * 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 = (int)src;   /* only need low bits */
               if ((t | (int)dst) & wmask) {
                       /*
                        * Try to align operands.  This cannot be done
                        * unless the low bits match.
                        */
                       if ((t ^ (int)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 = *(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 = (int)src;
               if ((t | (int)dst) & wmask) {
                       if ((t ^ (int)dst) & wmask || length <= wsize)
                               t = length;
                       else
                               t &= wmask;
                       length -= t;
                       TLOOP1(*--dst = *--src);
               }
               t = length / wsize;
               TLOOP(src -= wsize; dst -= wsize; *(word *)dst = *(word *)src);
               t = length & wmask;
               TLOOP(*--dst = *--src);
       }
#ifdef MEMCOPY
       return(dst0);
#else
#ifdef MEMMOVE
       return(dst0);
#else
       return;
#endif
#endif
}