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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 */

}