float comparison gives wrong result in loop?

[Bradley Smith]

Don Clugston wrote:
> Bradley Smith wrote:
>> With the following code, why does the assert fail?
> [snip]
> 
>> The loop exits early, but it should not. The result of
>> "j <= ( 1.0f / STEP_SIZE)" is somehow different in the while statement 
>> versus in the call to writefln.
>  > Interestingly, if the code is optimized, the assert passes.
> 
> Are you sure? Haven't you just removed the assert?

I don't think optimization removes asserts. Does it? If I'm wrong, that 
is an import fact to be aware of. However, if I insert "assert(false);", 
optimization doesn't remove it; so I assume asserts are not removed.


> import std.stdio;
> 
> void main() {
>     const float STEP_SIZE = 0.2f;
> 
>     float j = 0.0f;
>     real q;
>     while (j <=  ( 1.0f / STEP_SIZE)) {
>         j += 1.0f;
>         q = j;
>         writefln("%a %a %a", q, j, ( 1.0f / STEP_SIZE));
>         writefln(j <= ( 1.0f / STEP_SIZE));
>     }
>     float step2 = STEP_SIZE;
> 
>     assert(!(j <= ( 1.0f / step2))); // passes
>     assert(!(j <= ( 1.0f / STEP_SIZE))); // fails!
> }

That is a very interesting twist. I wouldn't expect that using a 
variable would be different than a constant. Can someone explain this?

Thanks,
   Bradley