From b72592e75fdecb34e2ac5f931730409a1fb68e8a Mon Sep 17 00:00:00 2001
From: Joseph Myers <joseph@codesourcery.com>
Date: Fri, 23 May 2014 12:07:50 +0000
Subject: Fix log10 (1) in round-downward mode (bug 16977).

As with various other issues of this kind, bug 16977 is log10 (1)
wrongly returning -0 rather than +0 in round-downward mode because of
an implementation effectively in terms of log1p (x - 1).  This patch
fixes the issue in the same way used for log.

Tested x86_64 and x86 and ulps updated accordingly.  Also tested for
mips64 to confirm a fix was needed for ldbl-128 and to validate that
fix (also applied to ldbl-128ibm since that version of logl is
essentially the same as the ldbl-128 one).

	[BZ #16977]
	* sysdeps/i386/fpu/e_log10.S (__ieee754_log10): Take absolute
	value when x - 1 is zero.
	* sysdeps/i386/fpu/e_log10f.S (__ieee754_log10f): Likewise.
	* sysdeps/i386/fpu/e_log10l.S (__ieee754_log10l): Likewise.
	* sysdeps/ieee754/ldbl-128/e_log10l.c (__ieee754_log10l): Return
	0.0L for an argument of 1.0L.
	* sysdeps/ieee754/ldbl-128ibm/e_log10l.c (__ieee754_log10l):
	Likewise.
	* sysdeps/x86_64/fpu/e_log10l.S (__ieee754_log10l): Take absolute
	value when x - 1 is zero.
	* math/libm-test.inc (log10_test): Use ALL_RM_TEST.
	* sysdeps/i386/fpu/libm-test-ulps: Update.
	* sysdeps/x86_64/fpu/libm-test-ulps: Likewise.
---
 sysdeps/i386/fpu/e_log10.S      |  8 +++++++-
 sysdeps/i386/fpu/e_log10f.S     |  8 +++++++-
 sysdeps/i386/fpu/e_log10l.S     |  8 +++++++-
 sysdeps/i386/fpu/libm-test-ulps | 24 ++++++++++++++++++++++++
 4 files changed, 45 insertions(+), 3 deletions(-)

(limited to 'sysdeps/i386')

diff --git a/sysdeps/i386/fpu/e_log10.S b/sysdeps/i386/fpu/e_log10.S
index ce6a81abb6..17277084ca 100644
--- a/sysdeps/i386/fpu/e_log10.S
+++ b/sysdeps/i386/fpu/e_log10.S
@@ -46,7 +46,13 @@ ENTRY(__ieee754_log10)
 	fnstsw			// x-1 : x : log10(2)
 	andb	$0x45, %ah
 	jz	2f
-	fstp	%st(1)		// x-1 : log10(2)
+	fxam
+	fnstsw
+	andb	$0x45, %ah
+	cmpb	$0x40, %ah
+	jne	5f
+	fabs			// log10(1) is +0 in all rounding modes.
+5:	fstp	%st(1)		// x-1 : log10(2)
 	fyl2xp1			// log10(x)
 	ret
 
diff --git a/sysdeps/i386/fpu/e_log10f.S b/sysdeps/i386/fpu/e_log10f.S
index 8c20723555..72a3b88251 100644
--- a/sysdeps/i386/fpu/e_log10f.S
+++ b/sysdeps/i386/fpu/e_log10f.S
@@ -47,7 +47,13 @@ ENTRY(__ieee754_log10f)
 	fnstsw			// x-1 : x : log10(2)
 	andb	$0x45, %ah
 	jz	2f
-	fstp	%st(1)		// x-1 : log10(2)
+	fxam
+	fnstsw
+	andb	$0x45, %ah
+	cmpb	$0x40, %ah
+	jne	5f
+	fabs			// log10(1) is +0 in all rounding modes.
+5:	fstp	%st(1)		// x-1 : log10(2)
 	fyl2xp1			// log10(x)
 	ret
 
diff --git a/sysdeps/i386/fpu/e_log10l.S b/sysdeps/i386/fpu/e_log10l.S
index cde987b137..45b9c6d21d 100644
--- a/sysdeps/i386/fpu/e_log10l.S
+++ b/sysdeps/i386/fpu/e_log10l.S
@@ -48,7 +48,13 @@ ENTRY(__ieee754_log10l)
 	fnstsw			// x-1 : x : log10(2)
 	andb	$0x45, %ah
 	jz	2f
-	fstp	%st(1)		// x-1 : log10(2)
+	fxam
+	fnstsw
+	andb	$0x45, %ah
+	cmpb	$0x40, %ah
+	jne	5f
+	fabs			// log10(1) is +0 in all rounding modes.
+5:	fstp	%st(1)		// x-1 : log10(2)
 	fyl2xp1			// log10(x)
 	ret
 
diff --git a/sysdeps/i386/fpu/libm-test-ulps b/sysdeps/i386/fpu/libm-test-ulps
index 946cad489b..1e89284455 100644
--- a/sysdeps/i386/fpu/libm-test-ulps
+++ b/sysdeps/i386/fpu/libm-test-ulps
@@ -1536,6 +1536,30 @@ Function: "log10":
 ildouble: 1
 ldouble: 1
 
+Function: "log10_downward":
+double: 1
+float: 1
+idouble: 1
+ifloat: 1
+ildouble: 1
+ldouble: 1
+
+Function: "log10_towardzero":
+double: 1
+float: 1
+idouble: 1
+ifloat: 1
+ildouble: 1
+ldouble: 1
+
+Function: "log10_upward":
+double: 1
+float: 1
+idouble: 1
+ifloat: 1
+ildouble: 1
+ldouble: 1
+
 Function: "log1p":
 ildouble: 1
 ldouble: 1
-- 
cgit 1.4.1