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/*
FUNCTION
        <<mempcpy>>---copy memory regions and return end pointer
 
ANSI_SYNOPSIS
        #include <string.h>
        void* mempcpy(void *<[out]>, const void *<[in]>, size_t <[n]>);
 
TRAD_SYNOPSIS
        void *mempcpy(<[out]>, <[in]>, <[n]>
        void *<[out]>;
        void *<[in]>;
        size_t <[n]>;
 
DESCRIPTION
        This function copies <[n]> bytes from the memory region
        pointed to by <[in]> to the memory region pointed to by
        <[out]>.
 
        If the regions overlap, the behavior is undefined.
 
RETURNS
        <<mempcpy>> returns a pointer to the byte following the
        last byte copied to the <[out]> region.
 
PORTABILITY
<<mempcpy>> is a GNU extension.
 
<<mempcpy>> requires no supporting OS subroutines.
 
	*/
 
#include <_ansi.h>
#include <stddef.h>
#include <limits.h>
#include <string.h>
 
/* Nonzero if either X or Y is not aligned on a "long" boundary.  */
#define UNALIGNED(X, Y) \
  (((long)X & (sizeof (long) - 1)) | ((long)Y & (sizeof (long) - 1)))
 
/* How many bytes are copied each iteration of the 4X unrolled loop.  */
#define BIGBLOCKSIZE    (sizeof (long) << 2)
 
/* How many bytes are copied each iteration of the word copy loop.  */
#define LITTLEBLOCKSIZE (sizeof (long))
 
/* Threshhold for punting to the byte copier.  */
#define TOO_SMALL(LEN)  ((LEN) < BIGBLOCKSIZE)
 
_PTR
_DEFUN (mempcpy, (dst0, src0, len0),
	_PTR dst0 _AND
	_CONST _PTR src0 _AND
	size_t len0)
{
#if defined(PREFER_SIZE_OVER_SPEED) || defined(__OPTIMIZE_SIZE__)
  char *dst = (char *) dst0;
  char *src = (char *) src0;
 
  while (len0--)
    {
      *dst++ = *src++;
    }
 
  return dst;
#else
  char *dst = dst0;
  _CONST char *src = src0;
  long *aligned_dst;
  _CONST long *aligned_src;
  int   len =  len0;
 
  /* If the size is small, or either SRC or DST is unaligned,
     then punt into the byte copy loop.  This should be rare.  */
  if (!TOO_SMALL(len) && !UNALIGNED (src, dst))
    {
      aligned_dst = (long*)dst;
      aligned_src = (long*)src;
 
      /* Copy 4X long words at a time if possible.  */
      while (len >= BIGBLOCKSIZE)
        {
          *aligned_dst++ = *aligned_src++;
          *aligned_dst++ = *aligned_src++;
          *aligned_dst++ = *aligned_src++;
          *aligned_dst++ = *aligned_src++;
          len -= BIGBLOCKSIZE;
        }
 
      /* Copy one long word at a time if possible.  */
      while (len >= LITTLEBLOCKSIZE)
        {
          *aligned_dst++ = *aligned_src++;
          len -= LITTLEBLOCKSIZE;
        }
 
       /* Pick up any residual with a byte copier.  */
      dst = (char*)aligned_dst;
      src = (char*)aligned_src;
    }
 
  while (len--)
    *dst++ = *src++;
 
  return dst;
#endif /* not PREFER_SIZE_OVER_SPEED */
}