glibc/sysdeps/generic/memmove.c

/* memmove -- copy memory to memory until the specified number of bytes
   has been copied.  Overlap is handled correctly.
   Copyright (C) 1991, 1995 Free Software Foundation, Inc.
   Contributed by Torbjorn Granlund (tege@sics.se).

The GNU C Library is free software; you can redistribute it and/or
modify it under the terms of the GNU Library General Public License as
published by the Free Software Foundation; either version 2 of the
License, or (at your option) any later version.

The GNU C Library 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
Library General Public License for more details.

You should have received a copy of the GNU Library General Public
License along with the GNU C Library; see the file COPYING.LIB.  If
not, write to the Free Software Foundation, Inc., 675 Mass Ave,
Cambridge, MA 02139, USA.  */

#include <ansidecl.h>
#include <string.h>
#include <memcopy.h>
#include <pagecopy.h>

/* All this is so that bcopy.c can #include
   this file after defining some things.  */
#ifndef	a1
#define	a1	dest	/* First arg is DEST.  */
#define	a1const
#define	a2	src	/* Second arg is SRC.  */
#define	a2const	CONST
#endif
#if	!defined(RETURN) || !defined(rettype)
#define	RETURN(s)	return (s)	/* Return DEST.  */
#define	rettype		PTR
#endif

rettype
DEFUN(memmove, (a1, a2, len),
      a1const PTR a1 AND a2const PTR a2 AND size_t len)
{
  unsigned long int dstp = (long int) dest;
  unsigned long int srcp = (long int) src;

  /* This test makes the forward copying code be used whenever possible.
     Reduces the working set.  */
  if (dstp - srcp >= len)	/* *Unsigned* compare!  */
    {
      /* Copy from the beginning to the end.  */

      /* If there not too few bytes to copy, use word copy.  */
      if (len >= OP_T_THRES)
	{
	  /* Copy just a few bytes to make DSTP aligned.  */
	  len -= (-dstp) % OPSIZ;
	  BYTE_COPY_FWD (dstp, srcp, (-dstp) % OPSIZ);

	  /* Copy whole pages from SRCP to DSTP by virtual address
	     manipulation, as much as possible.  */

	  PAGE_COPY_FWD_MAYBE (dstp, srcp, len, len);

	  /* Copy from SRCP to DSTP taking advantage of the known
	     alignment of DSTP.  Number of bytes remaining is put
	     in the third argumnet, i.e. in LEN.  This number may
	     vary from machine to machine.  */

	  WORD_COPY_FWD (dstp, srcp, len, len);

	  /* Fall out and copy the tail.  */
	}

      /* There are just a few bytes to copy.  Use byte memory operations.  */
      BYTE_COPY_FWD (dstp, srcp, len);
    }
  else
    {
      /* Copy from the end to the beginning.  */
      srcp += len;
      dstp += len;

      /* If there not too few bytes to copy, use word copy.  */
      if (len >= OP_T_THRES)
	{
	  /* Copy just a few bytes to make DSTP aligned.  */
	  len -= dstp % OPSIZ;
	  BYTE_COPY_BWD (dstp, srcp, dstp % OPSIZ);

	  /* Copy from SRCP to DSTP taking advantage of the known
	     alignment of DSTP.  Number of bytes remaining is put
	     in the third argumnet, i.e. in LEN.  This number may
	     vary from machine to machine.  */

	  WORD_COPY_BWD (dstp, srcp, len, len);

	  /* Fall out and copy the tail.  */
	}

      /* There are just a few bytes to copy.  Use byte memory operations.  */
      BYTE_COPY_BWD (dstp, srcp, len);
    }

  RETURN(dest);
}