Floating point optimizations
Sat Apr 5 21:26:00 GMT 2008
On Sat, Apr 5, 2008 at 9:06 AM, NightStrike <firstname.lastname@example.org> wrote:
> Wait, so are things like "c - (c - a)" optimized down to "a" or not? I
> use a lot of that in very time-intensive c++ code.
I think only if you tell it to be loose with requirements for applying
floating-point math optimizations (-ffast-math and related), since
DBL_MAX - (DBL_MAX-1) is, to the best of my knowledge, 0 --- not 1 ---
in IEEE math.
On the other hand, I managed to get >1 by adding DBL_EPSILON/10 to 1.0
repeatedly (though only on 1 of 4 computers on which I tried it) so my
intuitions could all be wrong.
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