Re: R: R: About hardfloat in ppc

[Yonggang Luo]

Question, in hard-float, if we don't want to read the fp register.

for example: If we wanna compute c = a + b in fp32

if c = a + b In hard float

and if b1 = c - a in hard float

if b1 != b at bitwise level, the we se the inexat to 1, otherwsie 

we set inexat bit to 0? are this valid?

we can also do it for a * b, a - b, a / b. 

On Thu, Apr 30, 2020 at 2:25 AM Alex Bennée <address@hidden> wrote:

Dino Papararo <address@hidden> writes:

> Hi Alex,
<snip>
>
> I leave to you TCG's experts how it works and how to implement it, I'm
> only tryng to explain a possible fast way to go (if ever possible) 😊

This is all a theoretical discussion unless someone cares enough to
improve the situation. While I have an interest in improving TCG
performance I'm afraid there are many more easier wins before tackling a
target specific hack for which I'm not familiar. No doubt this thread
will be referred to next time someone wants something done about it.

> ..Large majority of software don't check for exceptions at all and if
> I really want to pursue max precision I'll go for a software
> multiprecision library like GMP or MPFR Libraries.

However for QEMU we regard failure to correctly emulate the architecture
as a bug - we don't code to common software patterns because there is
plenty of software out there that doesn't follow it.

> So the hardfloats 'should' be set as first choice and only if
> instruction requires precision/error check process it in softfloats.

Sure but someone will have to do the work to support that.

--
Alex Bennée

--

         此致
礼
罗勇刚
Yours
    sincerely,
Yonggang Luo