Re: [Qemu-ppc] [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~