/* Copy memory to memory until the specified number of bytes
   has been copied.  Overlap is handled correctly.
   Copyright (C) 1991, 1995, 1996, 1997, 2003 Free Software Foundation, Inc.
   This file is part of the GNU C Library.
   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 Lesser General Public
   License as published by the Free Software Foundation; either
   version 2.1 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
   Lesser General Public License for more details.

   You should have received a copy of the GNU Lesser General Public
   License along with the GNU C Library; if not, write to the Free
   Software Foundation, Inc., 51 Franklin Street, Fifth Floor,
   Boston, MA  02110-1301  USA */

/*
 * August 2006. For Gawk: Borrowed from GLIBC and hacked unmercifully.
 * DON'T steal this for your own code, go straight to the GLIBC
 * source for the original versions.
 */


/* This stuff from libc/sysdeps/generic/memcopy.h */
typedef unsigned char byte;

/* Copy exactly NBYTES bytes from SRC_BP to DST_BP,
   without any assumptions about alignment of the pointers.  */
#define BYTE_COPY_FWD(dst_bp, src_bp, nbytes)				      \
  do									      \
    {									      \
      size_t __nbytes = (nbytes);					      \
      while (__nbytes > 0)						      \
	{								      \
	  byte __x = ((byte *) src_bp)[0];				      \
	  src_bp += 1;							      \
	  __nbytes -= 1;						      \
	  ((byte *) dst_bp)[0] = __x;					      \
	  dst_bp += 1;							      \
	}								      \
    } while (0)

/* Copy exactly NBYTES_TO_COPY bytes from SRC_END_PTR to DST_END_PTR,
   beginning at the bytes right before the pointers and continuing towards
   smaller addresses.  Don't assume anything about alignment of the
   pointers.  */
#define BYTE_COPY_BWD(dst_ep, src_ep, nbytes)				      \
  do									      \
    {									      \
      size_t __nbytes = (nbytes);					      \
      while (__nbytes > 0)						      \
	{								      \
	  byte __x;							      \
	  src_ep -= 1;							      \
	  __x = ((byte *) src_ep)[0];					      \
	  dst_ep -= 1;							      \
	  __nbytes -= 1;						      \
	  ((byte *) dst_ep)[0] = __x;					      \
	}								      \
    } while (0)

/* end of stuff from memcopy.h */

void *
memmove (dest, src, len)
     void *dest;
     const void *src;
     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 0 /* screw all this */
      /* 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 argument, 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.  */
#endif
      BYTE_COPY_FWD (dstp, srcp, len);
    }
  else
    {
      /* Copy from the end to the beginning.  */
      srcp += len;
      dstp += len;

#if 0 /* ditto */
      /* 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 argument, 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.  */
	}
#endif
      /* There are just a few bytes to copy.  Use byte memory operations.  */
      BYTE_COPY_BWD (dstp, srcp, len);
    }

  return (dest);
}