[PATCH 3/4] Use libc_fe* macros in ldbl-128/e_expl.c.

[Stefan Liebler]

On 3/25/20 4:42 PM, Adhemerval Zanella via Libc-alpha wrote:
> 
> 
> On 25/03/2020 12:07, Adhemerval Zanella wrote:
>>
>>
>> On 25/03/2020 12:00, Adhemerval Zanella wrote:
>>>
>>>
>>> On 25/03/2020 07:13, Stefan Liebler via Libc-alpha wrote:
>>>> Unfortunately, this patch is responsible for testfails on x86_64:
>>>>
>>>> math/test-float128-exp.out:
>>>> Failure: exp (-0x1p-10000): Exception "Underflow" set
>>>> Failure: exp (-0x2p-16384): Exception "Underflow" set
>>>> ...
>>>>
>>>> math/test-float128-cexp.out:
>>>> Failure: Real part of: cexp (0x2p-16384 - 0x4p-1076 i): Exception "Underflow" set
>>>> Failure: Real part of: cexp (0x2p-16384 - 0x8p-152 i): Exception "Underflow" set
>>>
>>> The sysdeps/x86/fpu/fenv_private.h states:
>>>
>>> 296 #ifdef __x86_64__
>>> 297 /* The SSE rounding mode is used by soft-fp (libgcc and glibc) on
>>> 298    x86_64, so that must be set for float128 computations.  */
>>> 299 # define SET_RESTORE_ROUNDF128(RM) \
>>> 300   SET_RESTORE_ROUND_GENERIC (RM, libc_feholdsetround_sse, libc_feresetround_sse)
>>>
>>> So
>>>
>>>>> diff --git a/sysdeps/ieee754/ldbl-128/e_expl.c b/sysdeps/ieee754/ldbl-128/e_expl.c
>>>>> index 37c1538c08..104ace1690 100644
>>>>> --- a/sysdeps/ieee754/ldbl-128/e_expl.c
>>>>> +++ b/sysdeps/ieee754/ldbl-128/e_expl.c
>>>>> @@ -66,6 +66,7 @@
>>>>>    #include <inttypes.h>
>>>>>    #include <math-barriers.h>
>>>>>    #include <math_private.h>
>>>>> +#include <fenv_private.h>
>>>>>    #include <math-underflow.h>
>>>>>    #include <stdlib.h>
>>>>>    #include "t_expl.h"
>>>>> @@ -146,9 +147,10 @@ __ieee754_expl (_Float128 x)
>>>>>          union ieee854_long_double ex2_u, scale_u;
>>>>>          fenv_t oldenv;
>>>>>    -      feholdexcept (&oldenv);
>>>>>    #ifdef FE_TONEAREST
>>>>> -      fesetround (FE_TONEAREST);
>>>>> +      libc_feholdexcept_setroundl (&oldenv, FE_TONEAREST);
>>>
>>> Should be libc_feholdexcept_setroundf128.
>>
>> But it does not see to help here, so I don't know what is failing as well.
> 
> Ok, so what is happening __sfp_handle_exceptions always use 387 exception
> mode for FP_EX_OVERFLOW and FP_EX_UNDERFLOW:
> 
> config/i386/sfp-exceptions.c
> 
>   79   if (_fex & FP_EX_OVERFLOW)
>   80     {
>   81       struct fenv temp;
>   82       asm volatile ("fnstenv\t%0" : "=m" (temp));
>   83       temp.__status_word |= FP_EX_OVERFLOW;
>   84       asm volatile ("fldenv\t%0" : : "m" (temp));
>   85       asm volatile ("fwait");
>   86     }
>   87   if (_fex & FP_EX_UNDERFLOW)
>   88     {
>   89       struct fenv temp;
>   90       asm volatile ("fnstenv\t%0" : "=m" (temp));
>   91       temp.__status_word |= FP_EX_UNDERFLOW;
>   92       asm volatile ("fldenv\t%0" : : "m" (temp));
>   93       asm volatile ("fwait");
>   94     }
> Yes this looks like the mentioned disassembly.
> Different that FP_EX_INEXACT, for instance, where __SSE_MATH__ sets
> whether SSE is used or not.
> 
> So I think it is not safe to use the SSE variants for libc_*_testf128,
> as for i387 we should use the default_* instead.
> 
I've just switched to default_* in sysdeps/x86/fpu/fenv_private.h:
-#ifdef __x86_64__
+#if 0
  /* The SSE rounding mode is used by soft-fp (libgcc and glibc) on
     x86_64, so that must be set for float128 computations.  */
  # define SET_RESTORE_ROUNDF128(RM) \

But now there are 7 testfails. For some of them, the max.ulp goes up 
(over 10), but there are even worse cases. Here are shortened excerpts 
of the out files:
- math/test-float128-clog.out:
Failure: Test: Real part of: clog_towardzero 
(0x2.82b795e420b281a934c6dd315cb2p-4 + 
0xf.cd42a15bf9a361243a89663e81e8p-4 i)
  ulp       :  162259276829213363391578010288127.0000
  max.ulp   :  3.0000
Failure: Test: Real part of: clog_upward 
(0x2.82b795e420b281a934c6dd315cb2p-4 + 
0xf.cd42a15bf9a361243a89663e81e8p-4 i)
  ulp       :  162259276829213363391578010288128.0000
  max.ulp   :  4.0000

- math/test-float128-clog10.out:
Failure: Test: Real part of: clog10_downward (0x3.bea2bd62e35p-4 + 
0xf.8e3d619a8d11bfd30b038eep-4 i)
  ulp       :  4.0000
  max.ulp   :  3.0000
Failure: Test: Real part of: clog10_towardzero 
(0x2.82b795e420b281a934c6dd315cb2p-4 + 
0xf.cd42a15bf9a361243a89663e81e8p-4 i)
  ulp       :  140936617129079063283494433422698.0000
  max.ulp   :  4.0000
Failure: Test: Real part of: clog10_upward 
(0x2.82b795e420b281a934c6dd315cb2p-4 + 
0xf.cd42a15bf9a361243a89663e81e8p-4 i)
  ulp       :  140936617129079063283494433422698.0000
  max.ulp   :  4.0000

- math/test-float128-jn.out
- math/test-float128-lgamma.out
- math/test-float128-tgamma.out:
something like:
  ulp       :  12.0000
  max.ulp   :  4.0000

Failure: tgamma_upward (-0x6.ec00000000000008p+8): errno set to 0, 
expected 34 (ERANGE)

- math/test-float128-y1.out:
Failure: Test: y1_downward (0x2p+0)
  ulp       :  13.0000
  max.ulp   :  4.0000
Failure: Test: y1_towardzero (0x2p+0)
  ulp       :  6.0000
  max.ulp   :  2.0000
Failure: Test: y1_upward (0x2p+0)
  ulp       :  10.0000
  max.ulp   :  5.0000

- math/test-float128-yn.out