[U-Boot] [PATCH 1/3] memcpy: use 32-bit copies if possible

[Joakim Tjernlund]

>
> Dear Alessandro Rubini,
>
> In message <20091008074114.GA30203 at mail.gnudd.com> you wrote:
> >
> > Since int is 32 also on 64bit systems, I used unsigned long.
>
> Note that this is not guaranteed, though. It could be 64 bit as well.
>
>
> >        /* do it one word at a time (32 bits or 64 bits) if possible */
> >        if ( ((count | (int)s) & (sizeof(long) - 1)) == 0) {
> >           count /= sizeof(long);
> >           cl = (c & 0xff) | ((c & 0xff) << 8);
> >           cl |= cl << 16;
> >           if (sizeof(long) > 4)
> >              cl |= cl << 32;
>
> How about:
>
>       cl = 0;
>       for (i=0; i<sizeof(long); ++i) {
>          cl <<= 8;
>          cl |= c & 0xff;
>       }
>
> GCC optimization will do the rest...

If you want gcc to optimise well, make it easy to do so.
Changing the for loop into:
      for (i=sizeof(long); i; --i)
makes it easier for gcc and more likely to result in optimal code.

Similarly for copy ops
 for(--top,--fromp, i = len/4; i; --i)
     *++top = *++fromp; /* pre incr can be one op on some archs */

   Jocke