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Re: [Patch-86512]: Subnormal float support in armv7(with -msoft-float) for intrinsics
- From: Umesh Kalappa <umesh dot kalappa0 at gmail dot com>
- To: Wilco Dijkstra <Wilco dot Dijkstra at arm dot com>
- Cc: gcc-patches at gcc dot gnu dot org, nd <nd at arm dot com>, Szabolcs Nagy <Szabolcs dot Nagy at arm dot com>, Ramana Radhakrishnan <Ramana dot Radhakrishnan at arm dot com>
- Date: Fri, 20 Jul 2018 21:30:10 +0530
- Subject: Re: [Patch-86512]: Subnormal float support in armv7(with -msoft-float) for intrinsics
- References: <DB5PR08MB10300230C683B33FB0297BDF83510@DB5PR08MB1030.eurprd08.prod.outlook.com>
Thank you all for your comments .
Wilco,
We tried some of the normalisation numbers and the fix works and please
could you help us with the input ,where if you see that fix breaks down.
Thank you again
~Umesh
On Fri, Jul 20, 2018, 7:07 PM Wilco Dijkstra <Wilco.Dijkstra@arm.com> wrote:
> Hi Umesh,
>
> Looking at your patch, this would break all results which need to be
> normalized.
>
>
> Index: libgcc/config/arm/ieee754-df.S
> ===================================================================
> --- libgcc/config/arm/ieee754-df.S (revision 262850)
> +++ libgcc/config/arm/ieee754-df.S (working copy)
> @@ -203,8 +203,11 @@
> #endif
>
> @ Determine how to normalize the result.
> + @ if result is denormal i.e (exp)=0,then don't normalise the
> result,
> LSYM(Lad_p):
> cmp xh, #0x00100000
> + blt LSYM(Lad_e)
> + cmp xh, #0x00100000
> bcc LSYM(Lad_a)
> cmp xh, #0x00200000
> bcc LSYM(Lad_e)
>
> It seems Lad_a doesn't correctly handle the case where the result is a
> denormal. For this case
> the result is correct so nothing else needs to be done. This requires an
> explicit test that the
> exponent is zero - other cases still need to be renormalized as usual.
> This code looks overly
> complex so any change will require extensive testing of all the corner
> cases.
>
> Wilco
>