/*********************************************************************************
 * Release:  1V00N00S00-R1-RC3
 * Filename: c/libc/string/memcpy.c
 *
 *********************************************************************************/

#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)

void* memcpy(void *dst0, const void *src0, size_t len0)
{
  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 dst0;
}
