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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