powerpc: refactor logb{f,l}

The power7 logb implementation does not show a performance gain on
ISA 2.07+ chips with faster floating-point to GRP instructions
(currently POWER8 and POWER9).

This patch moves the POWER7 implementation to generic one and enables
it for POWER7.  It also add some cleanup to use inline floating-point
number instead of define them using static const.

The performance difference is for POWER9:

  - Without patch:
  "logb": {
   "subnormal": {
    "duration": 4.99202e+09,
    "iterations": 8.83662e+08,
    "max": 75.194,
    "min": 5.501,
    "mean": 5.64925
   },
   "normal": {
    "duration": 4.97063e+09,
    "iterations": 9.97094e+08,
    "max": 46.489,
    "min": 4.956,
    "mean": 4.98512
   }
  }

  - With patch:
  "logb": {
   "subnormal": {
    "duration": 4.97226e+09,
    "iterations": 9.92036e+08,
    "max": 77.209,
    "min": 4.892,
    "mean": 5.01218
   },
   "normal": {
    "duration": 4.96192e+09,
    "iterations": 1.07545e+09,
    "max": 12.361,
    "min": 4.593,
    "mean": 4.61382
   }
  }

The ifunc implementation is also enabled only for powerpc64.

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/powerpc/power7/fpu/s_logb.c: Move to ...
	* sysdeps/powerpc/fpu/s_logb.c: ... here.  Use inline FP constants.
	* sysdeps/powerpc/power7/fpu/s_logbf.c: Move to ...
	* sysdeps/powerpc/fpu/s_logbf.c: ... here.  Use inline FP constants.
	* sysdeps/powerpc/power7/fpu/s_logbl.c: Move to ...
	* sysdeps/powerpc/fpu/s_logbl.c: ... here.  Use inline FP constants.
	* sysdeps/powerpc/powerpc32/power4/fpu/multiarch/s_logb-power7.c:
	Adjust implementation path.
	* sysdeps/powerpc/powerpc32/power4/fpu/multiarch/s_logbf-power7.c:
	Adjust implementation path.
	* sysdeps/powerpc/powerpc32/power4/fpu/multiarch/s_logbl-power7.c:
	Adjust implementation path.
	* sysdeps/powerpc/powerpc64/be/fpu/multiarch/Makefile
	(libm-sysdep_routines): Add s_log* objects.
	(CFLAGS-s_logbf-power7.c, CFLAGS-s_logbl-power7.c,
	CFLAGS-s_logb-power7.c): New fule.
	* sysdeps/powerpc/powerpc64/fpu/multiarch/s_logb-power7.c: Move
	to ...
	* sysdeps/powerpc/powerpc64/be/fpu/multiarch/s_logb-power7.c:
	... here.
	* sysdeps/powerpc/powerpc64/fpu/multiarch/s_logb-ppc64.c: Move
	to ...
	* sysdeps/powerpc/powerpc64/be/fpu/multiarch/s_logb-ppc64.c:
	... here.
	* sysdeps/powerpc/powerpc64/fpu/multiarch/s_logb.c: Move to ...
	* sysdeps/powerpc/powerpc64/be/fpu/multiarch/s_logb.c: ... here.
	* sysdeps/powerpc/powerpc64/fpu/multiarch/s_logbf-power7.c: Move
	to ...
	* sysdeps/powerpc/powerpc64/be/fpu/multiarch/s_logbf-power7.c:
	... here.
	* sysdeps/powerpc/powerpc64/fpu/multiarch/s_logbf-ppc64.c: Move
	to ...
	* sysdeps/powerpc/powerpc64/be/fpu/multiarch/s_logbf-ppc64.c:
	... here.
	* sysdeps/powerpc/powerpc64/fpu/multiarch/s_logbf.c: Move to ...
	* sysdeps/powerpc/powerpc64/be/fpu/multiarch/s_logbf.c: ... here.
	* sysdeps/powerpc/powerpc64/fpu/multiarch/s_logbl-power7.c: Move
	to ...
	* sysdeps/powerpc/powerpc64/be/fpu/multiarch/s_logbl-power7.c:
	... here.
	* sysdeps/powerpc/powerpc64/fpu/multiarch/s_logbl-ppc64.c: Move
	to ...
	* sysdeps/powerpc/powerpc64/be/fpu/multiarch/s_logbl-ppc64.c:
	... here.
	* sysdeps/powerpc/powerpc64/fpu/multiarch/s_logbl.c: Move to ...
	* sysdeps/powerpc/powerpc64/be/fpu/multiarch/s_logbl.c: ... here.
	* sysdeps/powerpc/powerpc64/fpu/multiarch/Makefile: Remove file.
	* sysdeps/powerpc/powerpc64/power7/fpu/s_logb.c: Remove file.
	* sysdeps/powerpc/powerpc64/power7/fpu/s_logbf.c: Likewise.
	* sysdeps/powerpc/powerpc64/power7/fpu/s_logbl.c: Likewise.

Reviewed-by: Gabriel F. T. Gomes <gabrielftg@linux.ibm.com>

1 files changed, 64 insertions, 0 deletions

diff --git a/sysdeps/powerpc/fpu/s_logb.c b/sysdeps/powerpc/fpu/s_logb.c
new file mode 100644
index 0000000000..364f7f0cc3
--- /dev/null
+++ b/sysdeps/powerpc/fpu/s_logb.c
@@ -0,0 +1,64 @@
+/* Get exponent of a floating-point value.  PowerPC version.
+   Copyright (C) 2012-2019 Free Software Foundation, Inc.
+   This file is part of the GNU C Library.
+
+   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/>.  */
+
+/* ISA 2.07 provides fast GPR to FP instruction (mfvsr{d,wz}) which make
+   generic implementation faster.  */
+#if defined(_ARCH_PWR8) || !defined(_ARCH_PWR7)
+# include <sysdeps/ieee754/dbl-64/s_logb.c>
+#else
+# include <math.h>
+# include <math_private.h>
+# include <math_ldbl_opt.h>
+# include <libm-alias-double.h>
+
+/* This implementation avoids FP to INT conversions by using VSX
+   bitwise instructions over FP values.  */
+double
+__logb (double x)
+{
+  double ret;
+
+  if (__glibc_unlikely (x == 0.0))
+    /* Raise FE_DIVBYZERO and return -HUGE_VAL[LF].  */
+    return -1.0 / fabs (x);
+
+  /* Mask to extract the exponent.  */
+  asm ("xxland %x0,%x1,%x2\n"
+       "fcfid  %0,%0"
+       : "=d" (ret)
+       : "d" (x), "d" (0x7ff0000000000000ULL));
+  ret = (ret * 0x1p-52) - 1023.0;
+  if (ret > 1023.0)
+    /* Multiplication is used to set logb (+-INF) = INF.  */
+    return (x * x);
+  else if (ret == -1023.0)
+    {
+      /* POSIX specifies that denormal numbers are treated as
+         though they were normalized.  */
+      int64_t ix;
+      EXTRACT_WORDS64 (ix, x);
+      ix &= UINT64_C (0x7fffffffffffffff);
+      return (double) (-1023 - (__builtin_clzll (ix) - 12));
+    }
+  /* Test to avoid logb_downward (0.0) == -0.0.  */
+  return ret == -0.0 ? 0.0 : ret;
+}
+# ifndef __logb
+libm_alias_double (__logb, logb)
+# endif
+#endif