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

[Stefan Liebler]

On 3/25/20 4:07 PM, Adhemerval Zanella via Libc-alpha 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.
> 
It does not help as this is already the case. The float128 exp is build 
with sysdeps/ieee754/float128/e_expf128.c which includes 
sysdeps/ieee754/float128/float128_private.h before including 
sysdeps/ieee754/ldbl-128/e_expl.c.

float128_private.h contains things like that:
...
#include <fenv_private.h>
...
#ifdef libc_feholdexcept_setroundf128
# undef libc_feholdexcept_setroundl
# define libc_feholdexcept_setroundl(ENV, RM)	\
   libc_feholdexcept_setroundf128 (ENV, RM)
#endif
...
#ifdef libc_fesetenvf128
# undef libc_fesetenvl
# define libc_fesetenvl(ENV) libc_fesetenvf128 (ENV)
#endif

>>
>>>> +#else
>>>> +      libc_feholdexceptl (&oldenv);
>>
>> And here libc_fesetenvf128.
>>
>>>>    #endif
>>>>            /* Calculate n.  */
>>>> @@ -198,7 +200,7 @@ __ieee754_expl (_Float128 x)
>>>>          math_force_eval (x22);
>>>>            /* Return result.  */
>>>> -      fesetenv (&oldenv);
>>>> +      libc_fesetenvl (&oldenv);
>>>>            result = x22 * ex2_u.d + ex2_u.d;
>>
>> It might require extend the libc_*f128 macros to other architectures
>> (not sure).
>>