Re: [PATCH 2/2] Add a missing default case in lgamma

[Paul Zimmermann <Paul.Zimmermann@inria.fr>]

       Dear Andoni,

unless I did a mistake, I still get the same error (7.50e+06 ulps)
than before this patch (after applying the other one), when I do an
exhaustive search on all binary32 inputs:

Using RedHat newlib
MPFR library: 4.1.0       
MPFR header:  4.1.0 (based on 4.1.0)
Checking function mylgammaf with MPFR_RNDN
libm wrong by up to 7.50e+06 ulp(s) [7497618] for x=-0x1.3a7fcap+1
mylgamma      gives -0x1p-24
mpfr_mylgamma gives -0x1.e4cf24p-24
Total: errors=509423944 (11.91%) errors2=11684280 maxerr=7.50e+06 ulp(s)

What result do you get for x=-0x1.3a7fcap+1?

Best regards,
Paul

> From: Andoni Arregi <andoni.arregui@gtd-gmbh.de>
> Date: Thu, 10 Feb 2022 17:12:40 +0100
> 
> The missing default case leads to large errors for |x| in range
> [2.0, 3.0[.
> In case of i=2, i.e., in the range between [2,3[, the computation
> "r += logf(z)" is not performed and hence the result was wrong.
> The added default case resolves this issue.
> (Courtesy of Andreas Jung, ESA)
> ---
>  newlib/libm/math/er_lgamma.c  | 1 +
>  newlib/libm/math/erf_lgamma.c | 1 +
>  2 files changed, 2 insertions(+)
> 
> diff --git a/newlib/libm/math/er_lgamma.c b/newlib/libm/math/er_lgamma.c
> index 5c88548fb..65727c6ab 100644
> --- a/newlib/libm/math/er_lgamma.c
> +++ b/newlib/libm/math/er_lgamma.c
> @@ -302,6 +302,7 @@ static double zero=  0.00000000000000000000e+00;
>  	   case 5: z *= (y+4.0);	/* FALLTHRU */
>  	   case 4: z *= (y+3.0);	/* FALLTHRU */
>  	   case 3: z *= (y+2.0);	/* FALLTHRU */
> +      default:
>  		   r += __ieee754_log(z); break;
>  	   }
>      /* 8.0 <= x < 2**58 */
> diff --git a/newlib/libm/math/erf_lgamma.c b/newlib/libm/math/erf_lgamma.c
> index 84d02159b..e7311cacf 100644
> --- a/newlib/libm/math/erf_lgamma.c
> +++ b/newlib/libm/math/erf_lgamma.c
> @@ -238,6 +238,7 @@ static float zero=  0.0000000000e+00;
>  	   case 5: z *= (y+(float)4.0);	/* FALLTHRU */
>  	   case 4: z *= (y+(float)3.0);	/* FALLTHRU */
>  	   case 3: z *= (y+(float)2.0);	/* FALLTHRU */
> +      default:
>  		   r += __ieee754_logf(z); break;
>  	   }
>      /* 8.0 <= x < 2**58 */
> -- 
> 2.35.1