Re: Reporting bugs: there is nothing to gain in frustrating reporters

[Vincent Lefevre <vincent+gcc at vinc17 dot org>]

On 2005-06-18 13:52:01 +0200, Toon Moene wrote:
> Vincent Lefevre wrote:
> 
> >Saying that the x86 processor is buggy is just completely silly.
> >Only some gcc developers think so.
> 
> No, Kahan thinks so too (sorry, can't come up with a link just right 
> now).

I'd be very interested in such a link. That would mean that he changed
his mind and it would contradict some points given in "How Java's FP
Hurt Everyone Everywhere". He even seems to like x87, see page 61 for
instance (though I disagree with him on the advantages of extended
precision, for portability reasons).

>  The original plan for x87 extended precision floating point was 
> to have a small stack of 80-bit floats on the chip, and an interrupt to 
> the OS if more registers were needed than the number extant on the chip. 
>  The OS was then to provide the extra storage to "feign" the unlimited 
> number of 80-bit "registers".
> 
> Unfortunately, somewhere in the design process of the 8087 things went 
> wrong and the chip only handles 8 80-bit registers, not providing an 
> interrupt (or any other support) to an OS to fake the "virtual" 80-bit 
> registers.
> 
> Hence our problems.

Why? Even when the 8-register limit isn't reached, there are problems.
And I recall the problem: the fact that an extended-precision value of
type double is not rounded to double-precision after an assignment or
a cast. I don't see the relation with the 8-register limit.

-- 
Vincent Lefèvre <vincent@vinc17.org> - Web: <http://www.vinc17.org/>
100% accessible validated (X)HTML - Blog: <http://www.vinc17.org/blog/>
Work: CR INRIA - computer arithmetic / SPACES project at LORIA