Re: MIPS checksum bug

["Maciej W. Rozycki" <macro@linux-mips.org>]

On Sat, 20 Sep 2008, Atsushi Nemoto wrote:

> @@ -229,6 +239,9 @@ LEAF(csum_partial)
>  
>       /* Still a full word to go  */
>       ulw     t1, (src)
> +#ifdef USE_DOUBLE
> +     add     t1, zero        /* clear upper 32bit */
> +#endif
>       PTR_ADDIU       src, 4
>       ADDC(sum, t1)
>  

 Unfortunately you can't zero-extend with a single instruction (you can
use a single sll(v) to sign-extend), unless the R2 ISA provides some
suitable oddity (which I haven't checked).  You want something like:

        dsll32  t1, t1, 0
        dsrl32  t1, t1, 0

instead.

  Maciej