From: Joseph Myers <joseph@codesourcery.com>
Date: Fri, 23 May 2014 12:07:50 +0000 (+0000)
Subject: Fix log10 (1) in round-downward mode (bug 16977).
X-Git-Tag: glibc-2.20~451
X-Git-Url: http://git.ipfire.org/cgi-bin/gitweb.cgi?a=commitdiff_plain;h=b72592e75fdecb34e2ac5f931730409a1fb68e8a;p=thirdparty%2Fglibc.git

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.
---

diff --git a/ChangeLog b/ChangeLog
index a7a9185e85e..c035c9f882b 100644
--- a/ChangeLog
+++ b/ChangeLog
@@ -1,3 +1,20 @@
+2014-05-23  Joseph Myers  <joseph@codesourcery.com>
+
+	[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.
+
 2014-05-23  Rasmus Villemoes  <rv@rasmusvillemoes.dk>
 
 	* manual/filesys.texi (Scanning Directory Content): Fix prototype of
diff --git a/NEWS b/NEWS
index 8aaf2f4cb5b..1c44fd6e2d4 100644
--- a/NEWS
+++ b/NEWS
@@ -18,7 +18,7 @@ Version 2.20
   16760, 16770, 16786, 16789, 16791, 16799, 16800, 16815, 16823, 16824,
   16831, 16838, 16849, 16854, 16876, 16877, 16885, 16888, 16890, 16912,
   16915, 16916, 16917, 16922, 16927, 16928, 16932, 16943, 16958, 16966,
-  16967, 16965.
+  16967, 16965, 16977.
 
 * The minimum Linux kernel version that this version of the GNU C Library
   can be used with is 2.6.32.
diff --git a/math/libm-test.inc b/math/libm-test.inc
index de7bc8ad940..0d467a21951 100644
--- a/math/libm-test.inc
+++ b/math/libm-test.inc
@@ -7798,9 +7798,7 @@ static const struct test_f_f_data log10_test_data[] =
 static void
 log10_test (void)
 {
-  START (log10, 0);
-  RUN_TEST_LOOP_f_f (log10, log10_test_data, );
-  END;
+  ALL_RM_TEST (log10, 0, log10_test_data, RUN_TEST_LOOP_f_f, END);
 }
 
 
diff --git a/sysdeps/i386/fpu/e_log10.S b/sysdeps/i386/fpu/e_log10.S
index ce6a81abb6e..17277084ca9 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 8c207235551..72a3b882518 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 cde987b137e..45b9c6d21d0 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 946cad489b5..1e892844550 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
diff --git a/sysdeps/ieee754/ldbl-128/e_log10l.c b/sysdeps/ieee754/ldbl-128/e_log10l.c
index b403f815fbe..618255f2fa3 100644
--- a/sysdeps/ieee754/ldbl-128/e_log10l.c
+++ b/sysdeps/ieee754/ldbl-128/e_log10l.c
@@ -193,6 +193,9 @@ __ieee754_log10l (long double x)
   if (hx >= 0x7fff000000000000LL)
     return (x + x);
 
+  if (x == 1.0L)
+    return 0.0L;
+
 /* separate mantissa from exponent */
 
 /* Note, frexp is used so that denormal numbers
diff --git a/sysdeps/ieee754/ldbl-128ibm/e_log10l.c b/sysdeps/ieee754/ldbl-128ibm/e_log10l.c
index 1a6a4a0fa3c..7477791b77a 100644
--- a/sysdeps/ieee754/ldbl-128ibm/e_log10l.c
+++ b/sysdeps/ieee754/ldbl-128ibm/e_log10l.c
@@ -195,6 +195,9 @@ __ieee754_log10l (long double x)
   if (hx >= 0x7ff0000000000000LL)
     return (x + x);
 
+  if (x == 1.0L)
+    return 0.0L;
+
 /* separate mantissa from exponent */
 
 /* Note, frexp is used so that denormal numbers
diff --git a/sysdeps/x86_64/fpu/e_log10l.S b/sysdeps/x86_64/fpu/e_log10l.S
index 6c07024c19c..2607ad199b8 100644
--- a/sysdeps/x86_64/fpu/e_log10l.S
+++ b/sysdeps/x86_64/fpu/e_log10l.S
@@ -46,7 +46,13 @@ 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/x86_64/fpu/libm-test-ulps b/sysdeps/x86_64/fpu/libm-test-ulps
index d47287696c6..bb549d2b0d7 100644
--- a/sysdeps/x86_64/fpu/libm-test-ulps
+++ b/sysdeps/x86_64/fpu/libm-test-ulps
@@ -1611,6 +1611,30 @@ ifloat: 2
 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":
 float: 1
 ifloat: 1