But beware that checking floating point numbers for equality is basically impossibe

But even if some real numbers cannot be exactly represented in binary, at least they are both exactly misrepresented in the same way, so checking for equality should still work.

I thought that this was only a problem if you were calculating with them:

print .2  == .2 ? 'equal' : 'not equal';
equal
print .2 *10 == 2 ? 'equal' : 'not equal';
equal
print .1999999999999999 *10 == 2 ? 'equal' : 'not equal';
not equal
print .19999999999999999 *10 == 2 ? 'equal' : 'not equal';
equal
print .20000000000000001 *10 == 2 ? 'equal' : 'not equal';
equal
print .2000000000000001 *10 == 2 ? 'equal' : 'not equal';
not equal
[download]

So on the Perl on my machine (AS Perl 5.8.8) .2 seems to be anything between .19999999999999999 and .20000000000000001.