math: Use wordsize-64 version for s_logb

  - The resulting binary difference on 32 bits architecture is
    minimum.  On i686-linux-gnu (with architecture optimization
    routine removed) there is no different using logb benchtests

  - It helps wordsize-64 architectures that use ldbl-opt.

  - It add some code simplification with reduction of duplicated
    implementations.

Checked on powerpc-linux-gnu (built without --with-cpu, with
--with-cpu=power4 and with --with-cpu=power5+ and --disable-multi-arch),
powerpc64-linux-gnu (built without --with-cp and with --with-cpu=power5+
and --disable-multi-arch).

	* sysdeps/ieee754/dbl-64/wordsize-64/s_logb.c: Move to ...
	* sysdeps/ieee754/dbl-64/s_logb.c: ... here.  Add work around for
	powerpc32 integer 0 converting to -0.

Reviewed-by: Gabriel F. T. Gomes <[email protected]>

ChangeLog

@@ -1,5 +1,9 @@
 2019-07-08  Adhemerval Zanella  <[email protected]>
 
+	* sysdeps/ieee754/dbl-64/wordsize-64/s_logb.c: Move to ...
+	* sysdeps/ieee754/dbl-64/s_logb.c: ... here.  Add work around for
+	powerpc32 integer 0 converting to -0.
+
 	* benchtests/Makefile (bench-math): Add logb.
 	* benchtests/logb-inputs: New file.
 	* benchtests/logbf-inputs: New file.

sysdeps/ieee754/dbl-64/s_logb.c

@@ -1,51 +1,48 @@
-/* @(#)s_logb.c 5.1 93/09/24 */
-/*
- * ====================================================
- * Copyright (C) 1993 by Sun Microsystems, Inc. All rights reserved.
- *
- * Developed at SunPro, a Sun Microsystems, Inc. business.
- * Permission to use, copy, modify, and distribute this
- * software is freely granted, provided that this notice
- * is preserved.
- * ====================================================
- */
+/* Compute radix independent exponent.
+   Copyright (C) 2011-2019 Free Software Foundation, Inc.
+   This file is part of the GNU C Library.
+   Contributed by Ulrich Drepper <[email protected]>, 2011.
 
-/*
- * double logb(x)
- * IEEE 754 logb. Included to pass IEEE test suite. Not recommend.
- * Use ilogb instead.
- */
+   The GNU C Library is free software; you can redistribute it and/or
+   modify it under the terms of the GNU Lesser General Public
+   License as published by the Free Software Foundation; either
+   version 2.1 of the License, or (at your option) any later version.
+
+   The GNU C Library is distributed in the hope that it will be useful,
+   but WITHOUT ANY WARRANTY; without even the implied warranty of
+   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
+   Lesser General Public License for more details.
+
+   You should have received a copy of the GNU Lesser General Public
+   License along with the GNU C Library; if not, see
+   <http://www.gnu.org/licenses/>.  */
 
 #include <math.h>
+
 #include <math_private.h>
 #include <libm-alias-double.h>
 #include <fix-int-fp-convert-zero.h>
 
 double
 __logb (double x)
 {
-  int32_t lx, ix, rix;
+  int64_t ix, ex;
 
-  EXTRACT_WORDS (ix, lx, x);
-  ix &= 0x7fffffff;             /* high |x| */
-  if ((ix | lx) == 0)
+  EXTRACT_WORDS64 (ix, x);
+  ix &= UINT64_C(0x7fffffffffffffff);
+  if (ix == 0)
     return -1.0 / fabs (x);
-  if (ix >= 0x7ff00000)
+  ex = ix >> 52;
+  if (ex == 0x7ff)
     return x * x;
-  if (__glibc_unlikely ((rix = ix >> 20) == 0))
+  if (__glibc_unlikely (ex == 0))
     {
-      /* POSIX specifies that denormal number is treated as
-         though it were normalized.  */
-      int ma;
-      if (ix == 0)
-	ma = __builtin_clz (lx) + 32;
-      else
-	ma = __builtin_clz (ix);
-      rix -= ma - 12;
+      int m = __builtin_clzll (ix);
+      ex -= m - 12;
     }
-  if (FIX_INT_FP_CONVERT_ZERO && rix == 1023)
+  if (FIX_INT_FP_CONVERT_ZERO && ex == 1023)
     return 0.0;
-  return (double) (rix - 1023);
+  return (double) (ex - 1023);
 }
 #ifndef __logb
 libm_alias_double (__logb, logb)