On Sun, 09 Jan 2011 20:39:12 -0500, Jonathan M Davis <[email protected]>
wrote:
On Sunday 09 January 2011 16:27:11 bearophile wrote:
A bug I've introduced once in my D code, are you able to spot it?
void main() {
double x = +0;
double y = -0;
}
The bug: 'y' isn't the desired double -0.0
To avoid this bug DMD may keep the -0 and +0 integer literals
represented
in two distinct ways, so they have two different values when/if assigned
to a floating point. (But here D will behave a little differently from
C).
An alternative is to just add a warning to DMD.
A third possibility is to just ignore this probably uncommon bug :-)
Bye,
bearophile
I didn't even know that there _was_ such as thing as + or - 0 (or 0.0).
I would
have considered it a no-op, being identical to 0 or 0.0, and expected it
to be
compiled out completely. I haven't a clue what -0.0 would even mean. But
I'm not
exactly an expert on floating point values, so presumably, there's some
weird
floating point thing that - affects.
-0.0 is an artifact of the floating point sign bit: i.e. there is a + and
- for each value, so naturally there's also + and - 0. The difference
isn't generally something you care about, as they are practically
identical except in bit pattern (i.e. assert( 0.0 == -0.0 )).
