Re: [Boost-users] [Numeric.Interval_Lib] typecasting behaviour

From: John Maddock (john_at_[hidden])
Date: 2006-10-19 05:06:31

tirath wrote:
> The query...
> Before I started using the library, I had this assumption: let A be a
> float with an exact representation (i.e. width=0). If we cast A to a
> double, the resulting double will have a non-zero width -
> specifically the width will be equal to the extra precision afforded
> to doubles vs floats.

I'm not familiar with the interval lib, but if a float is an exact value, 
then promoting it to a wider type will result in an exact value as well.  I 
assume what you're looking for is a way to say "here is a float, that is 
holding the nearest representable value, but is inexact (has up to 0.5ulp 
error)" ?  Then that error would propagate to the double as you expect.

John.