Le 21/08/2023 à 10:34, Laurent Vivier a écrit :
Le 20/08/2023 à 22:55, Keith Packard a écrit :
#include <stdio.h>
#include <stdint.h>
#define X 0x1p+16383l
#define Y 0x1p-16446l
static long double build_mul = X * Y;
static volatile long double x = X;
static volatile long double y = Y;
static void
dump_ld(const char *label, long double ld)
{
union {
long double d;
struct {
uint32_t exp:16;
uint32_t space:16;
uint32_t h;
uint32_t l;
};
} u;
u.d = ld;
printf("%12s: % -27La 0x%04x 0x%08x 0x%08x\n", label, u.d, u.exp, u.h,
u.l);
}
int main(void)
{
long double runtime_mul = x * y;
dump_ld("x", x);
dump_ld("y", y);
dump_ld("build_mul", build_mul);
dump_ld("runtime_mul", runtime_mul);
return 0;
}
FYI, result of this program on a real hardware (q800/m68040) is:
x: 0x8p+16380 0x7ffe 0x80000000 0x00000000
y: 0x0.000000000000001p-16386 0x0000 0x00000000 0x00000001
build_mul: 0x8p-66 0x3fc0 0x80000000 0x00000000
runtime_mul: 0x8p-66 0x3fc0 0x80000000 0x00000000
When I developped the FPU emulation I compared the result of QEMU and a real hardware using
https://github.com/vivier/m68k-testfloat and https://github.com/vivier/m68k-softfloat
Thanks,
Laurent
