x86 Floating Point Catastrophically Broken #449
Description
Hi,
This is totally unexpected, but we have found out that x86 floating point operations do not work correctly in the emulator. I have no idea how this is even possible.
The following very simple program does not print the correct output:
#include <stdio.h>
volatile double D = 0xFFFFFFFF;
int main(void) {
volatile unsigned U = (unsigned)D;
printf("%x\n", U);
return 0;
}
A more detailed test similarly fails:
#include <stdio.h>
// INCORRECT OUTPUT:
// D: 4294967295.000000, int: 7fffffff
// D: 4294967295.000000, unsigned: 7fffffff
// cvttsd2si: 7fffffff
// fisttp: 7fffffff
volatile double D = 0xFFFFFFFF;
int convertWithSSE2(double n) {
int result;
asm("cvttsd2si %1, %0" : "=r"(result) : "x"(n) :);
return result;
}
int convertWithFPU(double n) {
int result;
asm("fldl %1\n\t"
"fisttpl %0"
: "=m"(result)
: "m"(n)
: "st");
return result;
}
int main(void) {
volatile int x = (int)D;
printf("D: %f, int: %x\n", D, x);
volatile unsigned ux = (unsigned)D;
printf("D: %f, unsigned: %x\n", D, ux);
int u1 = convertWithSSE2(D);
printf("cvttsd2si: %x\n", u1);
int u2 = convertWithFPU(D);
printf("fisttp: %x\n", u2);
return 0;
}