Equality == comparisons with floating point numbers

[Abdulhaq]

>
> ... I thought I did, but now I'm up against an interesting 
> conundrum: while equality == comparison can fail here for 
> 32-bit, isIdentical comparison can fail even for 64-bit, 
> although only for the release-mode build.
>
> What's particularly odd is that if before calling 
> assert(isIdentical( ... )) I use writeln to print the value of 
> isIdentical(...) to the screen, then it prints true, and the 
> assertion passes.  If I don't have the print statement, then 
> the assert fails.
>
> I'm presuming that calling writefln to print the variable 
> involves it being taken off the FPU?

I'm just guessing now but it seems that you are in an area that 
changes depending on which compiler you are using (how does it 
compile the FP instructions, does it use SSE instructions, how is 
it checking equality) and which exact processor are you on, does 
it support IEEE754, does the compiler try to support IEEE754 
exactly? I haven't seen much in the forums about FP behaviour in 
e.g. dmd. E.g. how does it deal with the issues raised in 
http://www.cs.berkeley.edu/~wkahan/JAVAhurt.pdf? The people who 
know these things can found discussing them at 
http://forum.dlang.org/thread/khbodtjtobahhpzmadap@forum.dlang.org?page=3#post-l4rj5o:24292k:241:40digitalmars.com 
:-).

It's generally held that checking FP numbers for exact equality 
isn't practical and it's better to go for equality within a 
certain tolerance - any reason why you're not happy with that :-)?