On 2008-10-27, Bart Massey
Peter Gavin
writes: The reason for doing it this way is that e.g. 2.5 is exactly between 2 and 3, and rounding *up* every time would cause an uneven bias toward 3. To counteract that effect, rounding to the nearest even integer is used, which causes the half of the x.5 values to round up, and the other half to round down.
Everyone keeps providing this rationale, but of course if you want "half the values to round up and the other half down" it does just as well to round positive values up and negative values down.
Except, of course, that it is quite common to work with just positive numbers. Working just with numbers near (even + 0.5) or (odd + 0.5) is extremely rare.
I have written floating point code that depends on consistent rounding in the past. Being able to depend on round (1 + x) = 1 + round x is sometimes useful, but not possible for round-to-even.
Also not for round-up -- consider floating point values where the precision changes and it rounds differently than you, or the point where adjacent floating point values are now 2 apart. You basically can't depend on any nice behaviour once floating point enters the room. -- Aaron Denney -><-