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Re: [PATCH, PR61219]: Fix sNaN handling in ARM float to double conversion
- From: Ramana Radhakrishnan <ramana dot gcc at googlemail dot com>
- To: Aurelien Jarno <aurelien at aurel32 dot net>
- Cc: gcc-patches <gcc-patches at gcc dot gnu dot org>
- Date: Tue, 17 Jun 2014 23:29:01 +0100
- Subject: Re: [PATCH, PR61219]: Fix sNaN handling in ARM float to double conversion
- Authentication-results: sourceware.org; auth=none
- References: <20140518212338 dot GA16272 at volta dot rr44 dot fr>
- Reply-to: ramrad01 at arm dot com
On Sun, May 18, 2014 at 10:23 PM, Aurelien Jarno <aurelien@aurel32.net> wrote:
> On ARM soft-float, the float to double conversion doesn't convert a sNaN
> to qNaN as the IEEE Std 754 standard mandates:
>
> "Under default exception handling, any operation signaling an invalid
> operation exception and for which a floating-point result is to be
> delivered shall deliver a quiet NaN."
>
> Given the soft float ARM code ignores exceptions and always provides a
> result, a float to double conversion of a signaling NaN should return a
> quiet NaN. Fix this in extendsfdf2.
>
>
> 2014-05-18 Aurelien Jarno <aurelien@aurel32.net>
>
> PR target/61219
> * config/arm/ieee754-df.S (extendsfdf2): Convert sNaN to qNaN.
Ok if no regressions along with a testcase to catch this case please
and fixing the PR number
Sorry about the slow review.
Ramana
>
>
> Index: libgcc/config/arm/ieee754-df.S
> ===================================================================
> --- libgcc/config/arm/ieee754-df.S (revision 210588)
> +++ libgcc/config/arm/ieee754-df.S (working copy)
> @@ -473,11 +473,15 @@
> eorne xh, xh, #0x38000000 @ fixup exponent otherwise.
> RETc(ne) @ and return it.
>
> - teq r2, #0 @ if actually 0
> - do_it ne, e
> - teqne r3, #0xff000000 @ or INF or NAN
> + bics r2, r2, #0xff000000 @ isolate mantissa
> + do_it eq @ if 0, that is ZERO or INF,
> RETc(eq) @ we are done already.
>
> + teq r3, #0xff000000 @ check for NAN
> + do_it eq, t
> + orreq xh, xh, #0x00080000 @ change to quiet NAN
> + RETc(eq) @ and return it.
> +
> @ value was denormalized. We can normalize it now.
> do_push {r4, r5, lr}
> mov r4, #0x380 @ setup corresponding exponent
>
> --
> Aurelien Jarno GPG: 4096R/1DDD8C9B
> aurelien@aurel32.net http://www.aurel32.net