Fix POWER7 logb results for negative subnormals (bug 19375)

The optimized POWER7 logb implementation does not use the absolute
value of the word extracted from the input to apply the leading 0-bits
builtin (to ignore the float sign).  This patch fixes it by
clearing the signal bit in the resulting word.

It fixes the subnormal tests failures when running on POWER7 ou
newer chip.

Tested on powerpc64le (POWER8).

	[BZ# 19375]
	* sysdeps/powerpc/power7/fpu/s_logb.c (__logb): Fix return for
	negative subnormals.

diff --git a/ChangeLog b/ChangeLog
index 17b04cd..6cd6d72 100644 (file)
--- a/ChangeLog
+++ b/ChangeLog
@@ -1,3 +1,8 @@
+2015-12-17  Adhemerval Zanella  <adhemerval.zanella@linaro.org>
+
+       * sysdeps/powerpc/power7/fpu/s_logb.c (__logb): Fix return for
+       negative subnormals.
+
 2015-12-16  H.J. Lu  <hongjiu.lu@intel.com>
 
        * sysdeps/unix/sysv/linux/x86_64/sysdep.h

diff --git a/sysdeps/powerpc/power7/fpu/s_logb.c b/sysdeps/powerpc/power7/fpu/s_logb.c
index c5feb67..abd1c2a 100644 (file)
--- a/sysdeps/powerpc/power7/fpu/s_logb.c
+++ b/sysdeps/powerpc/power7/fpu/s_logb.c
@@ -58,6 +58,7 @@ __logb (double x)
       int ma;
 
       EXTRACT_WORDS (ix, lx, x);
+      ix &= 0x7fffffff;
       if (ix == 0)
        ma = __builtin_clz (lx) + 32;
       else