Fix i386/x86_64 log* (1) zero sign for -ffinite-math-only (bug 19213).

For the -ffinite-math-only versions of various x86_64 and x86 log*
functions, a zero result from log* (1) is returned with incorrect sign
in round-downward mode.  This patch fixes this in a similar way to the
previous fixes for the non-*_finite versions of the functions.

Tested for x86_64 and x86 (including an i586 build), together with a
patch that will be applied separately to enable the main libm-test.inc
tests for the finite-math-only functions.

	[BZ #19213]
	* sysdeps/i386/fpu/e_log.S (__log_finite): Ensure +0 is always
	returned for argument 1.
	* sysdeps/i386/fpu/e_logf.S (__logf_finite): Likewise.
	* sysdeps/i386/fpu/e_logl.S (__logl_finite): Likewise.
	* sysdeps/i386/i686/fpu/e_logl.S (__logl_finite): Likewise.
	* sysdeps/x86_64/fpu/e_log10l.S (__log10l_finite): Likewise.
	* sysdeps/x86_64/fpu/e_log2l.S (__log2l_finite): Likewise.
	* sysdeps/x86_64/fpu/e_logl.S (__logl_finite): Likewise.

9 files changed, 60 insertions, 8 deletions

diff --git a/ChangeLog b/ChangeLog
index 9c78a11722..95dae4bafa 100644
--- a/ChangeLog
+++ b/ChangeLog
@@ -1,5 +1,15 @@
 2015-11-05  Joseph Myers  <joseph@codesourcery.com>
 
+	[BZ #19213]
+	* sysdeps/i386/fpu/e_log.S (__log_finite): Ensure +0 is always
+	returned for argument 1.
+	* sysdeps/i386/fpu/e_logf.S (__logf_finite): Likewise.
+	* sysdeps/i386/fpu/e_logl.S (__logl_finite): Likewise.
+	* sysdeps/i386/i686/fpu/e_logl.S (__logl_finite): Likewise.
+	* sysdeps/x86_64/fpu/e_log10l.S (__log10l_finite): Likewise.
+	* sysdeps/x86_64/fpu/e_log2l.S (__log2l_finite): Likewise.
+	* sysdeps/x86_64/fpu/e_logl.S (__logl_finite): Likewise.
+
 	[BZ #19211]
 	* math/bits/math-finite.h (lgamma): Set signgam if [__USE_MISC ||
 	__USE_XOPEN], not if [!__USE_ISOC99].
diff --git a/NEWS b/NEWS
index b462e85ddc..4e419980fe 100644
--- a/NEWS
+++ b/NEWS
@@ -22,7 +22,7 @@ Version 2.23
   19003, 19007, 19012, 19016, 19018, 19032, 19046, 19048, 19049, 19050,
   19059, 19071, 19074, 19076, 19077, 19078, 19079, 19085, 19086, 19088,
   19094, 19095, 19124, 19125, 19129, 19134, 19137, 19156, 19174, 19181,
-  19189, 19201, 19205, 19209, 19211, 19212.
+  19189, 19201, 19205, 19209, 19211, 19212, 19213.
 
 * A defect in the malloc implementation, present since glibc 2.15 (2012) or
   glibc 2.10 via --enable-experimental-malloc (2009), could result in the
diff --git a/sysdeps/i386/fpu/e_log.S b/sysdeps/i386/fpu/e_log.S
index 3fa32aad3c..335df22577 100644
--- a/sysdeps/i386/fpu/e_log.S
+++ b/sysdeps/i386/fpu/e_log.S
@@ -80,7 +80,13 @@ ENTRY(__log_finite)
 	fnstsw			// x-1 : x : log(2)
 	andb	$0x45, %ah
 	jz	2b
-	fstp	%st(1)		// x-1 : log(2)
+	fxam
+	fnstsw
+	andb	$0x45, %ah
+	cmpb	$0x40, %ah
+	jne	6f
+	fabs			// log(1) is +0 in all rounding modes.
+6:	fstp	%st(1)		// x-1 : log(2)
 	fyl2xp1			// log(x)
 	ret
 END(__log_finite)
diff --git a/sysdeps/i386/fpu/e_logf.S b/sysdeps/i386/fpu/e_logf.S
index ca83d39cef..de967a31f5 100644
--- a/sysdeps/i386/fpu/e_logf.S
+++ b/sysdeps/i386/fpu/e_logf.S
@@ -81,7 +81,13 @@ ENTRY(__logf_finite)
 	fnstsw			// x-1 : x : log(2)
 	andb	$0x45, %ah
 	jz	2b
-	fstp	%st(1)		// x-1 : log(2)
+	fxam
+	fnstsw
+	andb	$0x45, %ah
+	cmpb	$0x40, %ah
+	jne	6f
+	fabs			// log(1) is +0 in all rounding modes.
+6:	fstp	%st(1)		// x-1 : log(2)
 	fyl2xp1			// log(x)
 	ret
 END(__logf_finite)
diff --git a/sysdeps/i386/fpu/e_logl.S b/sysdeps/i386/fpu/e_logl.S
index 828e98aa8d..7a6d370e8f 100644
--- a/sysdeps/i386/fpu/e_logl.S
+++ b/sysdeps/i386/fpu/e_logl.S
@@ -84,7 +84,13 @@ ENTRY(__logl_finite)
 	fnstsw			// x-1 : x : log(2)
 	andb	$0x45, %ah
 	jz	2b
-	fstp	%st(1)		// x-1 : log(2)
+	fxam
+	fnstsw
+	andb	$0x45, %ah
+	cmpb	$0x40, %ah
+	jne	7f
+	fabs			// log(1) is +0 in all rounding modes.
+7:	fstp	%st(1)		// x-1 : log(2)
 	fyl2xp1			// log(x)
 	ret
 END(__logl_finite)
diff --git a/sysdeps/i386/i686/fpu/e_logl.S b/sysdeps/i386/i686/fpu/e_logl.S
index 0ccc8fc71e..e9ecbcd472 100644
--- a/sysdeps/i386/i686/fpu/e_logl.S
+++ b/sysdeps/i386/i686/fpu/e_logl.S
@@ -81,7 +81,13 @@ ENTRY(__logl_finite)
 	fcomip	%st(1)		// |x-1| : x-1 : x : log(2)
 	fstp	%st(0)		// x-1 : x : log(2)
 	jc	2b
-	fstp	%st(1)		// x-1 : log(2)
+	fxam
+	fnstsw
+	andb	$0x45, %ah
+	cmpb	$0x40, %ah
+	jne	6f
+	fabs			// log(1) is +0 in all rounding modes.
+6:	fstp	%st(1)		// x-1 : log(2)
 	fyl2xp1			// log(x)
 	ret
 END(__logl_finite)
diff --git a/sysdeps/x86_64/fpu/e_log10l.S b/sysdeps/x86_64/fpu/e_log10l.S
index 2607ad199b..8fa61644c1 100644
--- a/sysdeps/x86_64/fpu/e_log10l.S
+++ b/sysdeps/x86_64/fpu/e_log10l.S
@@ -79,7 +79,13 @@ ENTRY(__log10l_finite)
 	fnstsw			// x-1 : x : log10(2)
 	andb	$0x45, %ah
 	jz	2b
-	fstp	%st(1)		// x-1 : log10(2)
+	fxam
+	fnstsw
+	andb	$0x45, %ah
+	cmpb	$0x40, %ah
+	jne	6f
+	fabs			// log10(1) is +0 in all rounding modes.
+6:	fstp	%st(1)		// x-1 : log10(2)
 	fyl2xp1			// log10(x)
 	ret
 END(__log10l_finite)
diff --git a/sysdeps/x86_64/fpu/e_log2l.S b/sysdeps/x86_64/fpu/e_log2l.S
index c12906d456..a063255ddd 100644
--- a/sysdeps/x86_64/fpu/e_log2l.S
+++ b/sysdeps/x86_64/fpu/e_log2l.S
@@ -78,7 +78,13 @@ ENTRY(__log2l_finite)
 	fnstsw			// x-1 : x : 1
 	andb	$0x45, %ah
 	jz	2b
-	fstp	%st(1)		// x-1 : 1
+	fxam
+	fnstsw
+	andb	$0x45, %ah
+	cmpb	$0x40, %ah
+	jne	6f
+	fabs			// log2(1) is +0 in all rounding modes.
+6:	fstp	%st(1)		// x-1 : 1
 	fyl2xp1			// log(x)
 	ret
 END (__log2l_finite)
diff --git a/sysdeps/x86_64/fpu/e_logl.S b/sysdeps/x86_64/fpu/e_logl.S
index 047b8db88a..dbe6fd59dc 100644
--- a/sysdeps/x86_64/fpu/e_logl.S
+++ b/sysdeps/x86_64/fpu/e_logl.S
@@ -81,7 +81,13 @@ ENTRY(__logl_finite)
 	fnstsw			// x-1 : x : log(2)
 	andb	$0x45, %ah
 	jz	2b
-	fstp	%st(1)		// x-1 : log(2)
+	fxam
+	fnstsw
+	andb	$0x45, %ah
+	cmpb	$0x40, %ah
+	jne	7f
+	fabs			// log(1) is +0 in all rounding modes.
+7:	fstp	%st(1)		// x-1 : log(2)
 	fyl2xp1			// log(x)
 	ret
 END (__logl_finite)