Re: Everything You Know Is Wrong

[Bob Brown <bob@justplainbob.com>]

On 2016-03-02, Bob Brown <bob@justplainbob.com> wrote:
> On 2016-03-02, J-P. Rosen <rosen@adalog.fr> wrote:
>> Le 02/03/2016 16:44, Bob Brown a ?crit :
>>>> 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.
>> Well, true enough, I don't know for recent machines. Even Silicon
>> Graphics has disappeared (not so long ago), and AFAIK, they were not IEEE.
>>
>>>> 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.
>>> 
>> https://www.cs.berkeley.edu/~wkahan/JAVAhurt.pdf

Ok, skimming this quickly it does not seem to me that the issue was Java
requiring IEEE arithmetic. The issue was Java's implementation of IEEE
arithmetic is seriously broken and error prone. They did not support the
highest precision type even though it is in virtually all desktop
hardware. And they didn't support the various signalling and trap mechanisms
required (and provided by other languages) to protect against serious errors
in computations.

Furthermore, and this is well-known but only touched-on very briefly by
Kahan, the lack of integer math support in Java (and other very popular
scripting languages like Javascript) is a terribly wrong-headed notion that
causes no end of problems when floating point is misapplied and integer math
should have been used instead.

What's really scary is reading claims by various knuckelheads claiming it's
ok to do financial and accounting calculations with floating point...

Bob