Re: [PATCH v1 5/7] fpu/softfloat: avoid undefined behaviour when normalising empty sigs

From: Aleksandar Markovic <aleksandar.qemu.devel@gmail.com>
To: "Alex Bennée" <alex.bennee@linaro.org>
Cc: Peter Maydell <peter.maydell@linaro.org>,
	QEMU Developers <qemu-devel@nongnu.org>,
	Aurelien Jarno <aurelien@aurel32.net>
Subject: Re: [PATCH v1 5/7] fpu/softfloat: avoid undefined behaviour when normalising empty sigs
Date: Fri, 27 Mar 2020 12:13:48 +0200	[thread overview]
Message-ID: <CAHiYmc6kw1LYK=97zxvsKdY8VL4CgZMAcWGgRcuoEjHT=qX8zw@mail.gmail.com> (raw)
In-Reply-To: <20200327094945.23768-6-alex.bennee@linaro.org>

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11:53 Pet, 27.03.2020. Alex Bennée <alex.bennee@linaro.org> је написао/ла:
>
> The undefined behaviour checker

Alex, what exactly is "undefined behaviour checker"? If this is a test, can
you give us a link?

Sincerely,
Aleksandar

> pointed out that a shift of 64 would
> lead to undefined behaviour.
>
> Signed-off-by: Alex Bennée <alex.bennee@linaro.org>
> ---
>  fpu/softfloat.c | 11 ++++++++---
>  1 file changed, 8 insertions(+), 3 deletions(-)
>
> diff --git a/fpu/softfloat.c b/fpu/softfloat.c
> index 301ce3b537b..444d35920dd 100644
> --- a/fpu/softfloat.c
> +++ b/fpu/softfloat.c
> @@ -3834,9 +3834,14 @@ void normalizeFloatx80Subnormal(uint64_t aSig,
int32_t *zExpPtr,
>  {
>      int8_t shiftCount;
>
> -    shiftCount = clz64(aSig);
> -    *zSigPtr = aSig<<shiftCount;
> -    *zExpPtr = 1 - shiftCount;
> +    if (aSig) {
> +        shiftCount = clz64(aSig);
> +        *zSigPtr = aSig << shiftCount;
> +        *zExpPtr = 1 - shiftCount;
> +    } else {
> +        *zSigPtr = 0;
> +        *zExpPtr = 1 - 64;
> +    }
>  }
>
>
 /*----------------------------------------------------------------------------
> --
> 2.20.1
>
>

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