Re: [PATCH 06/28] powerpc: round/roundf refactor

["Gabriel F. T. Gomes" <gabriel@inconstante.eti.br>]

On Fri, Mar 29 2019, Adhemerval Zanella wrote:
> 
> 	* sysdeps/powerpc/fpu/round_to_integer.h (set_rounding_mode): Add
> 	ROUND handling.
> 	(round_to_integer_float): Likewise.

Similar to what I mentioned for the floor patch, just make sure you
mention the addition of the ROUND definition.

> diff --git a/sysdeps/powerpc/fpu/round_to_integer.h b/sysdeps/powerpc/fpu/round_to_integer.h
> index 77d9fc1f86..3fa2b77b6d 100644
> --- a/sysdeps/powerpc/fpu/round_to_integer.h
> +++ b/sysdeps/powerpc/fpu/round_to_integer.h
> @@ -38,6 +38,7 @@ set_fenv_mode (enum round_mode mode)
>    {
>    case CEIL:  rmode = FE_UPWARD; break;
>    case FLOOR: rmode = FE_DOWNWARD; break;
> +  case ROUND: rmode = FE_TOWARDZERO; break;
>    default:    rmode = FE_TONEAREST; break;
>    }

Likewise, check that the FLOOR definition is added to round_mode.

This patch looks good to me with these changes.

Reviewed-by: Gabriel F. T. Gomes <gabriel@inconstante.eti.br>


> @@ -60,12 +61,24 @@ round_to_integer_float (enum round_mode mode, float x)
>    set_fenv_mode (mode);
>    if (x > 0.0)
>      {
> +      /* IEEE 1003.1 round function.  IEEE specifies "round to the nearest
> +	 integer value, rounding halfway cases away from zero, regardless of
> +	 the current rounding mode."  However PowerPC Architecture defines
> +	 "Round to Nearest" as "Choose the best approximation. In case of a
> +	 tie, choose the one that is even (least significant bit o).".
> +	 So we can't use the PowerPC "Round to Nearest" mode. Instead we set
> +	 "Round toward Zero" mode and round by adding +-0.5 before rounding
> +	 to the integer value.  */
> +      if (mode == ROUND)
> +	r += 0.5f;
>        r += 0x1p+23;
>        r -= 0x1p+23;
>        r = fabs (r);
>      }
>    else if (x < 0.0)
>      {
> +      if (mode == ROUND)
> +	r -= 0.5f;
>        r -= 0x1p+23;
>        r += 0x1p+23;
>        r = -fabs (r);

OK.  Restored from the .S files.

> @@ -92,12 +105,16 @@ round_to_integer_double (enum round_mode mode, double x)
>    set_fenv_mode (mode);
>    if (x > 0.0)
>      {
> +      if (mode == ROUND)
> +	r += 0.5;
>        r += 0x1p+52;
>        r -= 0x1p+52;
>        r = fabs (r);
>      }
>    else if (x < 0.0)
>      {
> +      if (mode == ROUND)
> +	r -= 0.5;
>        r -= 0x1p+52;
>        r += 0x1p+52;
>        r = -fabs (r);

OK.  Likewise.

> +double
> +__round (double x)
> +{
> +#ifdef _ARCH_PWR5X
> +  return __builtin_round (x);
> +#else
> +  return round_to_integer_double (ROUND, x);
> +#endif
> +}

OK.  Arch check looks correct.

> -.LC1:	/* 0.5 */
> -	.long 0x3f000000
> -
> -/* double [fp1] round (double x [fp1])
> -   IEEE 1003.1 round function.  IEEE specifies "round to the nearest
> -   integer value, rounding halfway cases away from zero, regardless of
> -   the current rounding mode."  However PowerPC Architecture defines
> -   "Round to Nearest" as "Choose the best approximation. In case of a
> -   tie, choose the one that is even (least significant bit o).".
> -   So we can't use the PowerPC "Round to Nearest" mode. Instead we set
> -   "Round toward Zero" mode and round by adding +-0.5 before rounding
> -   to the integer value.  */
>
> [...]
>
> -#ifdef SHARED
> -	lfs	fp10,.LC1-.LC0(r9)
> -#else
> -	lis	r9,.LC1@ha
> -	lfs	fp10,.LC1@l(r9)
> -#endif
> -	ble-	cr6,.L4
> -	fadd	fp1,fp1,fp10	/* x+= 0.5;  */

OK.  Moved to round_to_integer_float and round_to_integer_double.