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Re: [PATCH] Implement fma correctly
On 10/13/2010 06:40 AM, Ulrich Drepper wrote:
> On Tue, Oct 12, 2010 at 18:02, Richard Henderson <rth@twiddle.net> wrote:
>> Given that you're already manipulating the status word, you
>> could go ahead and force 53-bit rounding at the same time
>> with minimal extra overhead. Of course, feupdateenv does
>> not reset the rounding size to match. You'd have to either
>> open-code that function in order avoid doing extra work,
>> or add new helper functions.
>
> I actually have second thoughts even about the fmaf code. The problem
> is that now libm is not signal-safe. There is no limitatino of using
> FP math in signal handlers and you now get different results depending
> on whether fmaf got interrupted or other code got interrupted.
>
> We might have to do everything in software only without appropriate
> fma hardware support.
The x86 kernel doesn't set up a known fpu state on signal entry?
That seems like a bug to be fixed to me.
r~