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Re: Simplify floating point conversions II
> On Wed, Nov 06, 2002 at 06:54:41PM +0100, Jan Hubicka wrote:
> > + For fast math it would be safe probably to convert (float)sqrt(x)
> > + into sqrt((float)x), but in strict mode the argument can overflow. */
> I don't believe this to be true.
What you don't believe? That in ffast-math we can do the transformation?
Right, that is possible. I am not sure whehter we can afford the
possible overflow there. So I can drop the comment.
> > + /* Wind away possible cast. */
> > + if (TREE_CODE (arg0) == NOP_EXPR)
> > + arg0 = TREE_OPERAND (arg0, 0);
> Why would you do this? This might be casting down to double from
> long double. You should only strip casts when they widen the type.
Right, I will add that. For some reason I believed that these are
> > + /* convert (outertype)((innertype0)a+(innertype1)b)
> > + into ((newtype)a+(newtype)b) where newtype
> > + is the widest mode from all of these. */
> This changes overflow characteristics of +. Consider
> (double)((float)a + (float)b)
> where A = B = 2**127. The result should be +Inf, not 2**128.
I am doing that only when the mode of + is wider.
> Finally, I think it is alarmingly incorrect that
> (float)((double)a + (double)b))
> does not result in a quantity of type float, as requested.
Here I do that. When a and b are floats, I will produce
is that wrong?