Re: Everything You Know Is Wrong

[Bob Brown <bob@justplainbob.com>]

On 2016-03-02, J-P. Rosen <rosen@adalog.fr> wrote:
> Le 02/03/2016 15:11, vincent.diemunsch@gmail.com a ?crit :
>> Here is the point about Ada : 
>> 
>> Remarkably enough, some languages don't clearly specify that if x is a
>> floating-point variable (with say a value of 3.0/10.0), then every occurrence
>> of (say) 10.0*x must have the same value. For example Ada, which is based
>> on Brown's model, seems to imply that floating-point arithmetic only has to
>> satisfy Brown's axioms, and thus expressions can have one of many possible
>> values. Thinking about floating-point in this fuzzy way stands in sharp
>> contrast to the IEEE model, where the result of each floating-point operation is
>> precisely defined. In the IEEE model, we can prove that (3.0/10.0)*10.0
>> evaluates to 3 (Theorem 7). In Brown's model, we cannot.
>> 
>> Maybe this could be a topic for a new revision of Ada ?
>
> This was a deliberate decision, to make Ada compatible with various
> floating point models. Many (most? all?) number crunching machines do
> not have IEEE arithmetic, 

Really? Which one(s) are you talking about? I didn't even know there were
any number crunchers aside from the sad ones made from a kid's pool full
of Intel chips stuck together with tape and glue. All the real stuff like
CDC/Cray has been gone for ages.

> and there has been famous papers claiming that Java requiring IEEE
> arithmetic was a huge mistake. 

I would be interested in seeing the references if you have them at hand.

Thank you,

Bob