On Fri, Jul 14, 2017 at 04:03:51PM +0100, Robin Murphy wrote:
> On 14/07/17 15:39, Robin Murphy wrote:
> > On 14/07/17 15:06, Mark Rutland wrote:
> >> add sp, sp, x0 // sp = orig_sp + orig_x0
> >> sub x0, sp, x0 // x0 = orig_sp
> >> < check >
> >> sub x0, sp, x0 // x0 = orig_x0
> >
> > Haven't you now forcibly cleared the top bit of x0 thanks to overflow?
>
> ...or maybe not. I still can't quite see it, but I suppose it must
> cancel out somewhere, since Mr. Helpful C Program[1] has apparently
> proven me mistaken :(
>
> I guess that means I approve!
>
> Robin.
>
> [1]:
> #include <assert.h>
> #include <stdint.h>
>
> int main(void) {
> for (int i = 0; i < 256; i++) {
> for (int j = 0; j < 256; j++) {
> uint8_t x = i;
> uint8_t y = j;
> y = y + x;
> x = y - x;
> x = y - x;
> y = y - x;
> assert(x == i && y == j);
> }
> }
> }
I guess we have our first Tested-by for this series. :)
Thanks for taking a look!
Mark.
