Re: [vox-tech] detecting overflows

[Micah Cowan <micah@cowMAPSanbox.com>]

On Mon, Mar 12, 2001 at 06:27:40PM -0800, Mark K. Kim wrote:
> On Mon, 12 Mar 2001 jdnewmil@dcn.davis.ca.us wrote:
> 
> > IEEE 754 includes provisions for overflow notification through NaNs or
> > flags, but most implementations seem to support these features poorly.
> 
> Err... shouldn't you get infinity if you overflow?:
> 

Not necessarily.  See the following, from the libc manual, detailing
the results of an overflow operation:

`Overflow'
     This exception is raised whenever the result cannot be
     represented
     as a finite value in the precision format of the destination.  If
     no trap occurs the result depends on the sign of the intermediate
     result and the current rounding mode (IEEE 754, section 7.3):
       1. Round to nearest carries all overflows to oo with the sign
     of
          the intermediate result.

       2. Round toward 0 carries all overflows to the largest
          representable finite number with the sign of the
          intermediate
          result.

       3. Round toward -oo carries positive overflows to the largest
          representable finite number and negative overflows to -oo.

       4. Round toward oo carries negative overflows to the most
          negative representable finite number and positive overflows
          to oo.

     Whenever the overflow exception is raised, the inexact exception
     is also raised.

-Micah