Re: [PATCH] x86-64: Add sinf with FMA

[Adhemerval Zanella <adhemerval dot zanella at linaro dot org>]

On 05/12/2017 14:56, H.J. Lu wrote:
> On Tue, Dec 5, 2017 at 5:47 AM, Adhemerval Zanella
> <adhemerval.zanella@linaro.org> wrote:
> 
>> And with a simple modification to avoid int to fp conversion:
>>
>> ---
>> diff --git a/sysdeps/ieee754/flt-32/s_sinf.c b/sysdeps/ieee754/flt-32/s_sinf.c
>> index 40d3d19..a2fd3cf 100644
>> --- a/sysdeps/ieee754/flt-32/s_sinf.c
>> +++ b/sysdeps/ieee754/flt-32/s_sinf.c
>> @@ -75,7 +75,7 @@ static const double invpio4_table[] = {
>>    0x1.0e4107cp-169
>>  };
>>
>> -static const int ones[] = { +1, -1 };
>> +static const double ones[] = { 1.0, -1.0 };
>>
>>  /* Compute the sine value using Chebyshev polynomials where
>>     THETA is the range reduced absolute value of the input
>> @@ -92,7 +92,7 @@ reduced (const double theta, const unsigned long int n,
>>    const double theta2 = theta * theta;
>>    /* We are operating on |x|, so we need to add back the original
>>       signbit for sinf.  */
>> -  int sign;
>> +  double sign;
>>    /* Determine positive or negative primary interval.  */
>>    sign = ones[((n >> 2) & 1) ^ signbit];
>>    /* Are we in the primary interval of sin or cos?  */
>> ---
>>
>> I get:
>>
>>   "sinf": {
>>    "": {
>>     "duration": 4.0015e+10,
>>     "iterations": 1.4535e+09,
>>     "max": 640.456,
>>     "min": 11.437,
>>     "mean": 27.5301
>>    }
>>
>> Which is roughly 3% on mean and 11.5% on min. I think we can improve it
>> even more by avoiding the int to fp conversion to get the sign right
>> and try operate with sign as double argument.
> 
> I tried it on Skylake with the current master.  Before:
> 
>   "sinf": {
>    "": {
>     "duration": 3.4044e+10,
>     "iterations": 1.9942e+09,
>     "max": 141.106,
>     "min": 7.704,
>     "mean": 17.0715
>    }
>   }
> 
> After:
> 
>   "sinf": {
>    "": {
>     "duration": 3.40665e+10,
>     "iterations": 2.03199e+09,
>     "max": 95.994,
>     "min": 7.704,
>     "mean": 16.765
>    }
>   }
> 
> Generic is faster than asm now:
> 
>   "sinf": {
>    "": {
>     "duration": 3.40417e+10,
>     "iterations": 1.87792e+09,
>     "max": 138.868,
>     "min": 8.546,
>     "mean": 18.1273
>    }
>   }
> 
> Can you submit your patch?

I will do it, thanks for checking this out.