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Re: [PATCH] Fix for logb/logbf/logbl (bz 13954/13955/13956)


On 05/25/2012 09:56 AM, Andreas Schwab wrote:
> diff --git a/sysdeps/ieee754/dbl-64/s_logb.c b/sysdeps/ieee754/dbl-64/s_logb.c
> index baa35e1..17aa94b 100644
> --- a/sysdeps/ieee754/dbl-64/s_logb.c
> +++ b/sysdeps/ieee754/dbl-64/s_logb.c
> @@ -34,10 +34,12 @@ __logb (double x)
>      {
>        /* POSIX specifies that denormal number is treated as
>           though it were normalized.  */
> -      int m1 = (ix == 0) ? 0 : __builtin_clz (ix);
> -      int m2 = (lx == 0) ? 0 : __builtin_clz (lx);
> -      int ma = (m1 == 0) ? m2 + 32 : m1;
> -      return -1022.0 + (double)(11 - ma);
> +      int ma;
> +      if (ix == 0)
> +	ma = __builtin_clz (lx) + 32;
> +      else
> +	ma = __builtin_clz (ix);
> +      rix -= ma - 12;
>      }
>    return (double) (rix - 1023);
>  }
> diff --git a/sysdeps/ieee754/flt-32/s_logbf.c b/sysdeps/ieee754/flt-32/s_logbf.c
> index 025c70d..e2b3aaa 100644
> --- a/sysdeps/ieee754/flt-32/s_logbf.c
> +++ b/sysdeps/ieee754/flt-32/s_logbf.c
> @@ -31,8 +31,7 @@ __logbf (float x)
>      {
>        /* POSIX specifies that denormal number is treated as
>           though it were normalized.  */
> -      int m = (ix == 0) ? 0 : __builtin_clz (ix);
> -      return -126.0 + (float)(8 - m);
> +      rix -= __builtin_clz (ix) - 9;
>      }
>    return (float) (rix - 127);
>  }
> diff --git a/sysdeps/ieee754/ldbl-128/s_logbl.c b/sysdeps/ieee754/ldbl-128/s_logbl.c
> index cf6003e..3ba67b7 100644
> --- a/sysdeps/ieee754/ldbl-128/s_logbl.c
> +++ b/sysdeps/ieee754/ldbl-128/s_logbl.c
> @@ -41,10 +41,12 @@ __logbl (long double x)
>      {
>        /* POSIX specifies that denormal number is treated as
>           though it were normalized.  */
> -      int m1 = (hx == 0) ? 0 : __builtin_clzll (hx);
> -      int m2 = (lx == 0) ? 0 : __builtin_clzll (lx);
> -      int ma = (m1 == 0) ? m2 + 64 : m1;
> -      return -16382.0 + (long double)(15 - ma);
> +      int ma;
> +      if (hx == 0)
> +	ma = __builtin_clzll (lx) + 64;
> +      else
> +	ma = __builtin_clzll (hx);
> +      ex -= ma - 16;
>      }
>    return (long double) (ex - 16383);
>  }
> diff --git a/sysdeps/ieee754/ldbl-128ibm/s_logbl.c b/sysdeps/ieee754/ldbl-128ibm/s_logbl.c
> index 678b6ca..9b0bd98 100644
> --- a/sysdeps/ieee754/ldbl-128ibm/s_logbl.c
> +++ b/sysdeps/ieee754/ldbl-128ibm/s_logbl.c
> @@ -38,10 +38,12 @@ __logbl (long double x)
>      {
>        /* POSIX specifies that denormal number is treated as
>           though it were normalized.  */
> -      int m1 = (hx == 0) ? 0 : __builtin_clzll (hx);
> -      int m2 = (lx == 0) ? 0 : __builtin_clzll (lx);
> -      int ma = (m1 == 0) ? m2 + 64 : m1;
> -      return -1022.0 + (long double)(11 - ma);
> +      int ma;
> +      if (hx == 0)
> +	ma = __builtin_clzll (lx) + 64;
> +      else
> +	ma = __builtin_clzll (hx);
> +      rhx -= ma - 12;
>      }
>    return (long double) (rhx - 1023);
>  }
> diff --git a/sysdeps/ieee754/ldbl-96/s_logbl.c b/sysdeps/ieee754/ldbl-96/s_logbl.c
> index d8ad4bc..4289be1 100644
> --- a/sysdeps/ieee754/ldbl-96/s_logbl.c
> +++ b/sysdeps/ieee754/ldbl-96/s_logbl.c
> @@ -38,10 +38,12 @@ __logbl (long double x)
>      {
>        /* POSIX specifies that denormal number is treated as
>           though it were normalized.  */
> -      int m1 = (ix == 0) ? 0 : __builtin_clz (ix);
> -      int m2 = (lx == 0) ? 0 : __builtin_clz (lx);
> -      int ma = (m1 == 0) ? m2 + 32 : m1;
> -      return -16382.0 - (long double)(ma);
> +      int ma;
> +      if (ix == 0)
> +	ma = __builtin_clz (lx) + 32;
> +      else
> +	ma = __builtin_clz (ix);
> +      es -= ma - 1;
>      }
>    return (long double) (es - 16383);
>  }
Indeed your version is a better approach.


-- 
Adhemerval Zanella Netto
  Software Engineer
  Linux Technology Center Brazil
  Toolchain / GLIBC on Power Architecture
  azanella@linux.vnet.ibm.com / azanella@br.ibm.com
  +55 61 8642-9890


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