riscv: fmax/fmin sNaN fix

RISC-V's FPU follows the IEEE spec, not the POSIX spec.  This patch
adds handling for sNaN cases where the two specs differ.

	* sysdeps/riscv/rvd/s_fmax.c (__fmax): Handle sNaNs correctly.
	* sysdeps/riscv/rvd/s_fmin.c (__fmin): Likewise.
	* sysdeps/riscv/rvf/s_fmaxf.c (__fmaxf): Likewise.
	* sysdeps/riscv/rvf/s_fminf.c (__fminf): Likewise.

On 20/02/18 02:57, DJ Delorie wrote:
> 
> RISC-V's FPU follows the IEEE spec, not the POSIX spec.  This patch
                            ^^^^^^^^^
which one?
(the next ieee revision will have different min/max operations)

On 02/20/2018 02:26 AM, Szabolcs Nagy wrote:
> On 20/02/18 02:57, DJ Delorie wrote:
>>
>> RISC-V's FPU follows the IEEE spec, not the POSIX spec.  This patch
>                            ^^^^^^^^^
> which one?
> (the next ieee revision will have different min/max operations)

The next (201x) one.

r~

On Tue, 20 Feb 2018, Szabolcs Nagy wrote:

> On 20/02/18 02:57, DJ Delorie wrote:
> > 
> > RISC-V's FPU follows the IEEE spec, not the POSIX spec.  This patch
>                            ^^^^^^^^^
> which one?
> (the next ieee revision will have different min/max operations)

The point (as per 
<https://sourceware.org/ml/libc-alpha/2018-01/msg01084.html>) is that fmax 
and fmin in TS 18661-1 bind to maxNum and minNum.  Those operations are to 
be removed in IEEE 754-2018 so the C functions will have semantics that no 
longer have a corresponding IEEE operation (much like e.g. nextafter / 
nexttoward, which correspond to the Nextafter operation recommended in 
IEEE 754-1985 but removed in IEEE 754-2008).  Instead, the new minimum, 
minimumNumber, maximum and maximumNumber operations are proposed to have 
new functions fminimum, fminimum_num, fmaximum, fmaximum_num (and likewise 
*mag* functions) - but so far there is no public draft of those proposed 
TS changes (which might in any case more likely be dealt with in the C2x 
process rather than through a new revision of the TS being produced).

On Mon, 19 Feb 2018 18:57:49 PST (-0800), dj@redhat.com wrote:
>
> RISC-V's FPU follows the IEEE spec, not the POSIX spec.  This patch
> adds handling for sNaN cases where the two specs differ.
>
> 	* sysdeps/riscv/rvd/s_fmax.c (__fmax): Handle sNaNs correctly.
> 	* sysdeps/riscv/rvd/s_fmin.c (__fmin): Likewise.
> 	* sysdeps/riscv/rvf/s_fmaxf.c (__fmaxf): Likewise.
> 	* sysdeps/riscv/rvf/s_fminf.c (__fminf): Likewise.
>
> diff --git a/sysdeps/riscv/rvd/s_fmax.c b/sysdeps/riscv/rvd/s_fmax.c
> index ef8f1344ce..22e91bfc4b 100644
> --- a/sysdeps/riscv/rvd/s_fmax.c
> +++ b/sysdeps/riscv/rvd/s_fmax.c
> @@ -17,12 +17,19 @@
>     <http://www.gnu.org/licenses/>.  */
>
>  #include <math.h>
> +#include <math_private.h>
>  #include <libm-alias-double.h>
>
>  double
>  __fmax (double x, double y)
>  {
> -  asm ("fmax.d %0, %1, %2" : "=f" (x) : "f" (x), "f" (y));
> -  return x;
> +  double res;
> +
> +  if (__glibc_unlikely ((_FCLASS (x) | _FCLASS (y)) & _FCLASS_SNAN))
> +    return x + y;
> +  else
> +    asm ("fmax.d %0, %1, %2" : "=f" (res) : "f" (x), "f" (y));
> +
> +  return res;
>  }
>  libm_alias_double (__fmax, fmax)
> diff --git a/sysdeps/riscv/rvd/s_fmin.c b/sysdeps/riscv/rvd/s_fmin.c
> index c6ff24cefb..7b35230cac 100644
> --- a/sysdeps/riscv/rvd/s_fmin.c
> +++ b/sysdeps/riscv/rvd/s_fmin.c
> @@ -17,12 +17,19 @@
>     <http://www.gnu.org/licenses/>.  */
>
>  #include <math.h>
> +#include <math_private.h>
>  #include <libm-alias-double.h>
>
>  double
>  __fmin (double x, double y)
>  {
> -  asm ("fmin.d %0, %1, %2" : "=f" (x) : "f" (x), "f" (y));
> -  return x;
> +  double res;
> +
> +  if (__glibc_unlikely ((_FCLASS (x) | _FCLASS (y)) & _FCLASS_SNAN))
> +    return x + y;
> +  else
> +    asm ("fmin.d %0, %1, %2" : "=f" (res) : "f" (x), "f" (y));
> +
> +  return res;
>  }
>  libm_alias_double (__fmin, fmin)
> diff --git a/sysdeps/riscv/rvf/s_fmaxf.c b/sysdeps/riscv/rvf/s_fmaxf.c
> index 3293f2f41c..63f7e3d664 100644
> --- a/sysdeps/riscv/rvf/s_fmaxf.c
> +++ b/sysdeps/riscv/rvf/s_fmaxf.c
> @@ -17,12 +17,19 @@
>     <http://www.gnu.org/licenses/>.  */
>
>  #include <math.h>
> +#include <math_private.h>
>  #include <libm-alias-float.h>
>
>  float
>  __fmaxf (float x, float y)
>  {
> -  asm ("fmax.s %0, %1, %2" : "=f" (x) : "f" (x), "f" (y));
> -  return x;
> +  float res;
> +
> +  if (__glibc_unlikely ((_FCLASS (x) | _FCLASS (y)) & _FCLASS_SNAN))
> +    return x + y;
> +  else
> +    asm ("fmax.s %0, %1, %2" : "=f" (res) : "f" (x), "f" (y));
> +
> +  return res;
>  }
>  libm_alias_float (__fmax, fmax)
> diff --git a/sysdeps/riscv/rvf/s_fminf.c b/sysdeps/riscv/rvf/s_fminf.c
> index e4411f04b2..82cca4e37d 100644
> --- a/sysdeps/riscv/rvf/s_fminf.c
> +++ b/sysdeps/riscv/rvf/s_fminf.c
> @@ -17,12 +17,19 @@
>     <http://www.gnu.org/licenses/>.  */
>
>  #include <math.h>
> +#include <math_private.h>
>  #include <libm-alias-float.h>
>
>  float
>  __fminf (float x, float y)
>  {
> -  asm ("fmin.s %0, %1, %2" : "=f" (x) : "f" (x), "f" (y));
> -  return x;
> +  float res;
> +
> +  if (__glibc_unlikely ((_FCLASS (x) | _FCLASS (y)) & _FCLASS_SNAN))
> +    return x + y;
> +  else
> +    asm ("fmin.s %0, %1, %2" : "=f" (res) : "f" (x), "f" (y));
> +
> +  return res;
>  }
>  libm_alias_float (__fmin, fmin)

Also looks good, modulo the commit message and ChangeLog.  Thanks!