Guillaume Melquiond wrote:
Le lundi 15 mai 2006 à 12:10 -0700, Robert Ramey a écrit :
Peter Dimov wrote:
It depends. Where do you draw the line? Is inf a number? Is -0.0 a number? You have to have NaN if you want to be able to represent x/y as a float.
That's the problem. x/y is not a valid operation if y is equal to 0. So it can't be represented as a number.
The fact that C++ permits such an operation makes C++ different than arithmetic. The fact that C++ uses operators like "/" and defines them similar to - but not identical to - the way they are defined by standard arithmetic is the source of all these problems. I say that C++ should be changed to so that the floats and operators which apply to them should implement what people expect from arithmetic operators.
"Standard arithmetic" defines infinitely precise operators on real numbers. You cannot be seriously suggesting that C++ should stop using floating-point numbers and switch to such an arithmetic.
of course not.
The C++ float type is a *floating-point* type and as such it obeys the rules of *floating-point* arithmetic. Whatever your expectations, you cannot do anything about the fact that floating-point numbers have a limited range and a limited precision. Because of those, they are unable to obey the rules of a standard arithmetic (whatever it is).
I don't expect undefined operations to produce results. That's what most C++ implementations do. I expect that - as in "standard arithmetic" I get some sort of exception when I invoke an undefined operation. That's what my desk calculator does and it seems reasonable to me. Much better than just returning a bogus value to be used in the next operation. Robert Ramey