text: /* Copy memory to memory until the specified number of bytes
     has been copied.  Overlap is handled correctly.
     Copyright (C) 1991-2018 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, see
     <http://www.gnu.org/licenses/>.  */
  
  #include <memcopy.h>
  #include <string.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
  #undef memmove
  #endif
  #if !defined(RETURN) || !defined(rettype)
  #define RETURN(s) return (s) /* Return DEST.  */
  #define rettype void *
  #endif
  
  #ifndef MEMMOVE
  #define MEMMOVE memmove
  #endif
  
  rettype MEMMOVE(a1const void *a1, a2const void *a2, 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 MEMCPY_OK_FOR_FWD_MEMMOVE
  		dest = memcpy(dest, src, len);
  #else
  		/* 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.  */
  		BYTE_COPY_FWD(dstp, srcp, len);
  #endif /* MEMCPY_OK_FOR_FWD_MEMMOVE */
  	}
  	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 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.  */
  		}
  
  		/* There are just a few bytes to copy.  Use byte memory operations.  */
  		BYTE_COPY_BWD(dstp, srcp, len);
  	}
  
  	RETURN(dest);
  }
  