revised motion # 20 for July 19-20

[David Hough 754R work <754r@xxxxxxxxxxx>]

revised to fit current draft:

Motion: clarify conversion to unsigned integer format - plan A - After rounding

Rationale: On June 21 we discussed various approaches to this problem.
The one certain thing is that the draft is unclear.
This motion removes one aspect of that uncertainty.
The text parallels that of case 8.
 
Text:
In section 9.2, add an item to the list of invalid operations:
 
   l)  Conversion of an internal floating-point number, which would
       convert to a negative signed integer under the prevailing
       rounding mode,
       to an unsigned integer format and this cannot otherwise be indicated.
 
Commentary:
An alternative formulation
 
   l)  Conversion of an internal floating-point number, strictly less than 
zero,       to an unsigned integer format and this cannot otherwise be 
indicated.
 
is based on the proposition that you shouldn't be converting a negative
number to an unsigned format.
However this is unlike the case of conversion to a signed integer, which
is invariably treated as "after rounding."
 
An even more alternative formulation, when going to twos complement unsigned,
is to have no exceptions for finite arguments, and deliver (at potentially
extravagant cost) the correct result, modulo 2^n.