Re: [patch][0/5] powerpc: Add support to fully comply with IEEE-754 standard

[Kumar Gala <galak@kernel.crashing.org>]

On Jan 25, 2007, at 2:25 AM, Zhu Ebony-r57400 wrote:

>
>> No, I think the round handler should try to do the rounding
>> by hand.
>> Since you have the non rounded information provided by HW,
>> its much simpler to just do the rounding step.
>
> Hi Kumar,
>
> I have some new thoughts about rounding handler.
> Suppose we set SPEFSCR[FRMC]=0b10 (rounding towards +Inf) and
> a normal "efsmul" may generate rounding interrupt. At this time,
> according
> to manual, unrounded (truncated) result is placed in the target
> register. Please
> note the target register contains a hexadecimal representation of a
> floating point number. Since it represents a floating point number
> exactly
> so we can not round it anymore.

I don't follow what you mean by not being able to round it anymore.

> Maybe we still need to emulate the whole "efsmul" instruction by
> software.

You can't always do that.  Think about the following instruction:

	efsmul	r3, r3, r3

You'll have lost the original value of r3 when the exception occurs.

- k