Vincent Lefevre wrote:
On 2005-05-24 09:04:11 +0200, Uros Bizjak wrote:
I would like to point out that for applications that crunch data
from real world (no infinites or nans, where precision is not
critical) such as various simulations, -ffast-math is something that
can speed up application a lot.
But note that even when precision is not critical, you may get
consistency problems or annoying unintuitive side effects. For
instance, see
http://gcc.gnu.org/bugzilla/show_bug.cgi?id=15134
where
float x = 30.0;
int main()
{
if ( 90.0/x != 3.0)
abort();
return 0;
}
fails with -ffast-math (on x86). I would not recommend it, unless
the user knows all the consequences.
On the other hand, in general using != and == on floating point numbers
is always dangerous if you do not know all the consequences. For
example, on your above program if I use 30.1 and 90.3, the program fails
without -ffast-math.
Chris
