Re: [PATCH] Update powerpc libm-test-ulps

[Adhemerval Zanella <adhemerval.zanella@linaro.org>]

On 20/08/2020 15:39, Carlos O'Donell wrote:
> On 8/20/20 2:37 PM, Matheus Castanho via Libc-alpha wrote:
>> Before this patch, the following tests were failing:
>>
>> ppc and ppc64:
>>     FAIL: math/test-ldouble-j0
>>
>> ppc64le:
>>     FAIL: math/test-ibm128-j0
>> ---
>>  sysdeps/powerpc/fpu/libm-test-ulps | 4 ++--
>>  1 file changed, 2 insertions(+), 2 deletions(-)
>>
>> diff --git a/sysdeps/powerpc/fpu/libm-test-ulps b/sysdeps/powerpc/fpu/libm-test-ulps
>> index cd2a5fed45..0b82c3f107 100644
>> --- a/sysdeps/powerpc/fpu/libm-test-ulps
>> +++ b/sysdeps/powerpc/fpu/libm-test-ulps
>> @@ -1317,13 +1317,13 @@ Function: "j0_downward":
>>  double: 2
>>  float: 4
>>  float128: 4
>> -ldouble: 11
>> +ldouble: 12
>>  
>>  Function: "j0_towardzero":
>>  double: 5
>>  float: 6
>>  float128: 2
>> -ldouble: 8
>> +ldouble: 16
> 
> We should not have ULPs higher than 9.
> 
> I see Adhemerval added some 11 ULPs here for cexp.
> 
> We should be able to achieve <= 9 ULPs on these algorithms, otherwise there are
> compiler problems that need fixing?

We are more forgiving for IBM long double due its inherent precision issues:

math/libm-test-support.c

 228   if (testing_ibm128)
 229     /* The documented accuracy of IBM long double division is 3ulp
 230        (see libgcc/config/rs6000/ibm-ldouble-format), so do not
 231        require better accuracy for libm functions that are exactly
 232        defined for other formats.  */
 233     max_valid_error = exact ? 3 : 16;
 234   else
 235     max_valid_error = exact ? 0 : 9;

And jN implementation also has low precision for some inputs.  With both constraints
I think 16ulps should be ok.