Re: [gnugo-devel] The killer heuristic

[Evan Berggren Daniel]

OK, I get the same results.  I'll look into it a bit more, I think...
very weird.  However, one thing I've had repeated to me a number of times:
never, but never, do equality tests on floating point numbers.  This is a
weirder example than most, though.  GNU Go doesn't do equality tests in
the connection code, though, does it?

The usual example of fp weirdness I've seen is the following:

float i = 0.0;
while (i != 1.0) {
        i += 0.1;
}

which will repeat forever.  However, the cause of that is easily explained
by repeating binary numbers being added.

Evan

On Sun, 26 Jan 2003, Arend Bayer wrote:

> Evan wrote:
>
> > Floating point rounding problems is an interesting thought...  is there a
> > way to compile things to do IEEE floating point instead of platform
> > dependent, to test this out?
>
> Well gcc has an option -mieee-fp but I doubt this works.
>
> Try the example program below. I consistently get "not equal" as result
> (also with -mieee-fp). When compiling this with -O2, the executable
> doesn't even contain the string "the same" anymore, as this branch gets
> optimized away.
>
> I don't know IEEE, so either this is IEEE-correct (which means that IEEE
> doesn't do what one (at least me) would naively expect it to do), or
> this should be considered a compiler bug.
>
> Arend
>
>
> #include <stdio.h>
> #include <unistd.h>
>
> int
> main()
> {
>       float x = 1.0;
>       float y = 1.0/3.0;
>
>       if (x / 3.0 == y)
>                       fprintf(stdout, "the same\n");
>       else
>                       fprintf(stdout, "not equal\n");
>       return 0;
> }
>
>
>
>
>
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