Re: It All Comes Down to the IBM 704

In article <1120916134.777467.284420@xxxxxxxxxxxxxxxxxxxxxxxxxxxx> jsavard@xxxxxxxxx writes:
> *** T. Winter wrote:
....
> > I have no idea in what sense the exponent can be viewed as being in
> > excess-n notation. See the following table (the exponent field is
> > given in octal):
> > field exponent
> > 3777 infinite
> > 3776 1022
> > 2001 1
> > 2000 0
> > 1777 indefinite
> > 1776 -1
> > 0001 -1022
> > 0000 -1023
....
> I thought the table was something like this:
>
> 2001400000000000 1
> 2000400000000000 0.5
> 1777400000000000 0.25

I think you should reread. 0.25 is 177640000000000. When the exponent
field is 1777 the f.p. number is undefined (a special class).

> It seems you're referring to the "unpacked" form of the exponent. When
> the numbers are packed, that is, converted to the form in which they
> are actually stored in memory, minus zero is moved to the outer end of
> the exponent range.

No, I am referring to the packed form. If (as you state) in the packed
form "undefined" would be moved to the outer end of the range that would
mean that an exponent field of "0000" is "undefined", but that is false.

> Or at least that is how I initially understood it. But perhaps it
> requires closer examination.

Yes, do. I do not have a manual here at home, so I can not quote.
--
*** t. winter, cwi, kruislaan 413, 1098 sj amsterdam, nederland, +31205924131
home: bovenover 215, 1025 jn amsterdam, nederland; http://www.cwi.nl/~***/
.