Re: is Vax addressing sane today

On Sat, 21 Sep 2024 01:52:32 +0000, MitchAlsup1 wrote:

On Sat, 21 Sep 2024 1:09:43 +0000, Lawrence D'Oliveiro wrote:
 

On Fri, 20 Sep 2024 22:00:28 +0000, MitchAlsup1 wrote:
>

But then IEEE 754 exception semantics make even less sense than Linux
signals. ...

>
Note that what IEEE 754 calls an “exception” is just a bunch of status
bits reporting on the current state of the computation: there is no
implication of some transfer of control elsewhere.

 
Then how do you implement the alternate exception model ??? which IS
part of 754-2008 and 754-2019

Section 8.3 of the 2008 spec says:

    NOTE 2 — Immediate alternate exception handling for an exception
    can be implemented by traps or, for exceptions listed in Clause 7
    other than underflow, by testing status flags after each operation
    or at the end of the associated block. Thus for exceptions listed
    in Clause 7 other than underflow, immediate exception handling can
    be implemented with the same mechanism as delayed exception
    handling, if no better implementation mechanism is available.

So explicit testing of flag bits is permitted. Note that the special case
for underflow mentioned is that the exception signalled is “inexact”, not
“underflow”.