On Tue, Oct 28, 2008 at 04:07:12PM +0000, Bart Massey wrote:
I'm just saying that the name "round" is unfortunate, since there's no single universally accepted mathematical definition for it. For this reason many programming languages either don't provide it or provide a different version. The names "roundHalfUp" and "roundHalfEven" are much better: they each correspond to a well-known mathematical function that is codified in an IEEE standards document.
If it were up to me, I'd deprecate round in Haskell' and make the documentation point to these other rounding functions.
Our solution in Nickle (http://nickle.org), BTW, was to provide floating point with user-settable mantissa precision and a default precision of 256 bits. For all practical purposes we know of, this makes worrying about the edge cases for rounding pointless. Kahan has a nice paper on this that I can't find right now.
Isn't it quite common to have numbers like 0.5 as input? (as an example of a number that's exactly representable in any binary floating point format, but whose rounded value depends on rounding convention. I don't feel strongly on the question, but was somewhat surprised to find that round is present, for the reasons you mention. floor (x+0.5) is not a bad way to round... no one will mistakenly thing that it'll do something smart with half-integers. David