[Libclc-dev] [PATCH v2 1/1] rootn: Flush denormals if not supported.

[Aaron Watry via Libclc-dev]

Am I being dense or just lucky (device supports denormals?)..  This
already passed on my RX580 before I applied your patch

I'm currently rebuilding new newer llvm on my r600 box that hopefully
won't segfault when running rootn to test there.

--Aaron

On Mon, Apr 30, 2018 at 1:05 PM, Jan Vesely via Libclc-dev
<libclc-dev at lists.llvm.org> wrote:
> On Tue, 2018-04-24 at 12:31 -0400, Jan Vesely wrote:
>> It's OK to either flush to 0 or return denormal result if the device
>> does not support denormals. See sec 7.2 and 7.5.3 of OCL specs
>>
>> v2: Use 0.0f explicitly intead of relying on GPU to flush it.
>>
>> Fixes CTS on carrizo and turks
>> Signed-off-by: Jan Vesely <jan.vesely at rutgers.edu>
>> ---
>> This removes the need for the second patch
>>  generic/lib/math/clc_rootn.cl | 11 +----------
>>  1 file changed, 1 insertion(+), 10 deletions(-)
>>
>> diff --git a/generic/lib/math/clc_rootn.cl b/generic/lib/math/clc_rootn.cl
>> index d7ee185..0a2c98d 100644
>> --- a/generic/lib/math/clc_rootn.cl
>> +++ b/generic/lib/math/clc_rootn.cl
>> @@ -170,16 +170,7 @@ _CLC_DEF _CLC_OVERLOAD float __clc_rootn(float x, int ny)
>>      tv = USE_TABLE(exp_tbl_ep, j);
>>
>>      float expylogx = mad(tv.s0, poly, mad(tv.s1, poly, tv.s1)) + tv.s0;
>> -    float sexpylogx;
>> -    if (!__clc_fp32_subnormals_supported()) {
>> -             int explg = ((as_uint(expylogx) & EXPBITS_SP32 >> 23) - 127);
>> -             m = (23-(m + 149)) == 0 ? 1: m;
>> -             uint mantissa =  ((as_uint(expylogx) & MANTBITS_SP32)|IMPBIT_SP32) >> (23-(m + 149));
>> -             sexpylogx = as_float(mantissa);
>> -    } else {
>> -             sexpylogx = expylogx * as_float(0x1 << (m + 149));
>> -    }
>> -
>> +    float sexpylogx = __clc_fp32_subnormals_supported() ? expylogx * as_float(0x1 << (m + 149)) : 0.0f;
>>
>>      float texpylogx = as_float(as_int(expylogx) + m2);
>>      expylogx = m < -125 ? sexpylogx : texpylogx;
> ping.
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