Precision and CD's

[Stephane Dalmas]

> > 
> > Other considerations:
> > 
> > The major advantage of floats/ bigfloats  is that the cost of
> > operations is mostly a function of the desired precision, and 
> > not (usually) the value. The usual
> > operations include sqrt, exp, log, sin, cos  etc. as well as +-*/.
> > 
> If that's what you consider the essence of bigfloats, then the
> representation should include a specification for the precision -- but
> several people on the list (including you) have argued vehemently against
> this: "bigfloats are exact rationals".

I may have miss a point or two in this discussion, but I agree with Richard
here. A bigfloat is an exact rational, but it is subject to a strange
arithmetic that is NOT the arithmetic on rational numbers. 


           Stéphane.

PS Not all IEEE floating-point "values" are rationals as we know them. That
is a reason to have them primitive (at least the most common double
precision ones).