Re: S/360

Sven Pran wrote:
> "robin"  wrote
> ...............
>>> Other problems were corrected in a massive Engineering Change, which
>>> added a guard digit to double precision, added postnormalization to
the
>>> halve instructions HER and HDR, and changed the results returned in
>>> cases of overflow and underflow.
>> Are you sure of that?  The 1964 Principles of Operations
>> states that a zero word is returned for underflow,
>> which it always did.
> 
> Has the handling of exponent underflow not always been under control of
> the PSW Program mask for exponent underflow like it is today?

Trapping or not trapping was always under control of the mask, but 
before the great Engineering Change, the stored value was always true 
zero, no matter which way the mask was set.

-- 
John W. Kennedy
"But now is a new thing which is very old--
that the rich make themselves richer and not poorer,
which is the true Gospel, for the poor's sake."
   -- Charles Williams.  "Judgement at Chelmsford"