On Sat, 5 Jul 2003, Beman Dawes wrote: > fpt_abs may do a unary "-" operation. I'm assuming, perhaps incorrectly, > that is essentially subtraction and subject to a possible rounding error.
I don't think there is a system where the opposite of a representable number would not be a representable number. So there should be no rounding error when changing signs. At least not with IEEE-754 floating point numbers. Moreover, 0-x may lead to results different from -x. So changing sign is essantially "not" a subtraction :-). Guillaume PS: for those who wonder how 0-x can be different from -x, think about exceptional cases like x=0 or x=NaN. _______________________________________________ Unsubscribe & other changes: http://lists.boost.org/mailman/listinfo.cgi/boost
