On Tue, 2008-11-11 at 13:32 -0800, R. Baker Kearfott wrote:
Van et al,
What's sacred about 1ULP? Might the programmer know the accuracy, which
isn't necessarily 1ULP? Such a case would be an argument in favor of
perhaps supplying a conversion of two floats, one representing the
midpoint, and the other representing the accuracy (in the form of
a radius, say). Thus, we WOULD have two conversion routines, one
for midpoint-radius, and one for lower bound and upper bound.
For an FP number not known to be exact, the closest to exact it can be
is 1/2 ulp each way.
Connecting these conversions to programming languages is a separate
issue. Do we want the two routines defined at the 1788 operation
level, or at the programming language level?
I think conversions beyond what P754 specifies belong at the programming
language level.
The P1788 standard should say "An interval is represented by two
floating-point numbers; the first is the lower bound of the interval and
the second is the upper bound."