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

["Alex Bennée" <alex.bennee@linaro.org>]

Aleksandar Markovic <aleksandar.qemu.devel@gmail.com> writes:

> 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?

It's enabled by our sanitizers build:

  ../../configure --cc=clang-8 --cxx=clang++-8 --enable-sanitizers

>
> 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
>>
>>


-- 
Alex Bennée