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.

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].

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

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)

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)

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)

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)

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)

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)

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)