Why doesn't C have unsigned floats?

Question

I know, the question seems to be strange. Programmers sometimes think too much. Please read on...

In C I use signed and unsigned integers a

Answer 1

Unsigned integer types in C are defined in such a way as to obey the rules of an abstract algebraic ring. For example, for any value X and Y, adding X-Y to Y will yield X. Unsigned integer types are guaranteed to obey these rules in all cases which do not involve conversion to or from any other numeric type [or unsigned types of different sizes], and that guarantee is one of the most important feature of such types. In some cases, it's worthwhile to give up the ability to represent negative numbers in exchange for the extra guarantees only unsigned types can provide. Floating-point types, whether signed or not, cannot abide by all the rules of an algebraic ring [e.g. they cannot guarantee that X+Y-Y will equal X], and indeed IEEE doesn't even allow them to abide by the rules of an equivalence class [by requiring that certain values compare unequal to themselves]. I don't think an "unsigned" floating-point type could abide by any axioms which an ordinary floating-point type could not, so I'm not sure what advantages it would offer.