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/*

FUNCTION

        <<memmove>>---move possibly overlapping memory

INDEX

        memmove

ANSI_SYNOPSIS

        #include <string.h>

        void *memmove(void *<[dst]>, const void *<[src]>, size_t <[length]>);

TRAD_SYNOPSIS

        #include <string.h>

        void *memmove(<[dst]>, <[src]>, <[length]>)

        void *<[dst]>;

        void *<[src]>;

        size_t <[length]>;

DESCRIPTION

        This function moves <[length]> characters from the block of

        memory starting at <<*<[src]>>> to the memory starting at

        <<*<[dst]>>>. <<memmove>> reproduces the characters correctly

        at <<*<[dst]>>> even if the two areas overlap.

RETURNS

        The function returns <[dst]> as passed.

PORTABILITY

<<memmove>> is ANSI C.

<<memmove>> requires no supporting OS subroutines.

QUICKREF

        memmove ansi pure

*/

#include <string.h>

#include <_ansi.h>

#include <stddef.h>

#include <limits.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)

/*SUPPRESS 20*/

_PTR

_DEFUN (memmove, (dst_void, src_void, length),

        _PTR dst_void _AND

        _CONST _PTR src_void _AND

        size_t length)

{

#if defined(PREFER_SIZE_OVER_SPEED) || defined(__OPTIMIZE_SIZE__)

  char *dst = dst_void;

  _CONST char *src = src_void;

  if (src < dst && dst < src + length)

    {

      /* Have to copy backwards */

      src += length;

      dst += length;

      while (length--)

        {

          *--dst = *--src;

        }

    }

  else

    {

      while (length--)

        {

          *dst++ = *src++;

        }

    }

  return dst_void;

#else

  char *dst = dst_void;

  _CONST char *src = src_void;

  long *aligned_dst;

  _CONST long *aligned_src;

  int   len =  length;

  if (src < dst && dst < src + len)

    {

      /* Destructive overlap...have to copy backwards */

      src += len;

      dst += len;

      while (len--)

        {

          *--dst = *--src;

        }

    }

  else

    {

      /* Use optimizing algorithm for a non-destructive copy to closely

         match memcpy. 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_void;

#endif /* not PREFER_SIZE_OVER_SPEED */

}