On Oct 3, 2006, at 8:30 AM, Martin v. Löwis wrote:
> As Michael Hudson observed, this is difficult to implement, though:
> You can't distinguish between -0.0 and +0.0 easily, yet you should.
Of course you can. It's absolutely trivial. The only part that's even
*the least bit* sketchy in this is assuming that a double is 64 bits.
Practically speaking, that is true on all architectures I know of,
and if it's not guaranteed, it could easily be a 'configure' time check.
typedef union {
double d;
uint64_t i;
} rawdouble;
int isposzero(double a) {
rawdouble zero;
zero.d = 0.0;
rawdouble aa;
aa.d = a;
return aa.i == zero.i;
}
int main() {
if (sizeof(double) != sizeof(uint64_t))
return 1;
printf("%d\n", isposzero(0.0));
printf("%d\n", isposzero(-0.0));
}
James
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