On 29 May 2011 01:21, wren ng thornton wrote:
On 5/28/11 8:38 AM, Daniel Fischer wrote:
(By the way, non-negative, like the current positive, is not entirely true, for bounded signed integer types [with twos' complement representation], gcd minBound minBound = gcd minBound 0 = minBound< 0, should that special case be mentioned or should we ignore it like we currently do?)
That's a sticky issue, but one that needs to be documented. Given that the result is always positive with the exception of gcd 0 0, gcd minBound minBound, gcd minBound 0, and gcd 0 minBound, I think these corner cases should be specifically enumerated.
There is a difference: gcd 0 0 follows from a general rule, but the minBound ones are the sort of corner wierdness we get for using fixed-size types. (That is, the former should be mentioned as a non-obvious consequence, the latter as an exception/bug.) Incidentally, gcd (minBound::Int) n currently gives negative results for quite a few values of n.