Re: [Qemu-devel] [PATCH] fix fdiv instruction

[Richard Henderson]

On Mon, Jun 25, 2018, 08:23 G 3 <address@hidden> wrote:

> >
> > Try
> >
> >     uint64_t expected_answer = 0xffff0000deadbeef;
> >     ...
> >     c.i = expected_answer;
> >     asm volatile("fdiv %0, %1, %2" : "+f"(c.d) : "f"(1.0), "f"(0.0));
> >
> > to avoid depending on uninitialized data.  (This expected value is
> > an SNaN with a deadbeef marker Just to be Sure.)
> >
> >
> > r~
>
>
> Ok I made this program and tried it on my iMac G5 (PowerPC 970).
>
> #include <stdio.h>
> #include <stdint.h>
> #include <inttypes.h>
>
> // Used to convert unsigned integer <--> double
> union Converter
> {
>      double d;
>      uint64_t i;
> };
> typedef union Converter Converter;
>
> int main (int argc, const char * argv[]) {
>      Converter answer;
>      answer.i = 0xffff0000deadbeef;
>      //asm volatile("mtfsb1 27"); /* Set ZE bit */
>      asm volatile("fdiv %0, %1, %2" : "=f"(answer.d) : "f"(1.0),
> "f"(0.0));
>

Need +f for inout operand.
This didn't test what you expected.

r~