Fix __ieee754_logl (-LDBL_MAX) in FE_DOWNWARD mode (bug 17022).

This patch fixes __ieee754_logl (-LDBL_MAX) on x86_64 and x86 not to
subtract 1 from its argument and so cause spurious overflow in
FE_DOWNWARD mode.  (For any argument strictly less than -1, it doesn't
matter whether or not 1 is subtracted before computing log1p, as long
as the result doesn't overflow to -Inf.)

Tested x86_64 and x86.  (This particular case lacks test coverage,
since the testsuite doesn't cover -lieee, but it will be covered by
tests after the following patch to test pow in all rounding modes,
which was the context in which this bug was found.)

	[BZ #17022]
	* sysdeps/i386/fpu/e_logl.S (__ieee754_logl): Do not subtract 1
	from arguments -2 or below.
	* sysdeps/i386/i686/fpu/e_logl.S (__ieee754_logl): Likewise.
	* sysdeps/x86_64/fpu/e_logl.S (__ieee754_logl): Likewise.

5 files changed, 22 insertions, 5 deletions

diff --git a/ChangeLog b/ChangeLog
index 997cec6..3204c4e 100644
--- a/ChangeLog
+++ b/ChangeLog
@@ -1,3 +1,11 @@
+2014-06-18  Joseph Myers  <joseph@codesourcery.com>
+
+	[BZ #17022]
+	* sysdeps/i386/fpu/e_logl.S (__ieee754_logl): Do not subtract 1
+	from arguments -2 or below.
+	* sysdeps/i386/i686/fpu/e_logl.S (__ieee754_logl): Likewise.
+	* sysdeps/x86_64/fpu/e_logl.S (__ieee754_logl): Likewise.
+
 2014-06-18  Andreas Schwab  <schwab@suse.de>
 
 	[BZ #17062]
diff --git a/NEWS b/NEWS
index 429dba5..0c4d8bb 100644
--- a/NEWS
+++ b/NEWS
@@ -19,8 +19,8 @@ Version 2.20
   16791, 16796, 16799, 16800, 16815, 16823, 16824, 16831, 16838, 16849,
   16854, 16876, 16877, 16878, 16882, 16885, 16888, 16890, 16912, 16915,
   16916, 16917, 16922, 16927, 16928, 16932, 16943, 16958, 16965, 16966,
-  16967, 16977, 16978, 16984, 16990, 16996, 17009, 17031, 17042, 17048,
-  17058, 17062.
+  16967, 16977, 16978, 16984, 16990, 16996, 17009, 17022, 17031, 17042,
+  17048, 17058, 17062.
 
 * The minimum Linux kernel version that this version of the GNU C Library
   can be used with is 2.6.32.
diff --git a/sysdeps/i386/fpu/e_logl.S b/sysdeps/i386/fpu/e_logl.S
index edae1d7..828e98a 100644
--- a/sysdeps/i386/fpu/e_logl.S
+++ b/sysdeps/i386/fpu/e_logl.S
@@ -40,8 +40,11 @@ ENTRY(__ieee754_logl)
 	fld	%st		// x : x : log(2)
 	sahf
 	jc	3f		// in case x is NaN or +-Inf
+	movzwl	4+8(%esp), %eax
+	cmpl	$0xc000, %eax
+	jae	6f		// x <= -2, avoid overflow from -LDBL_MAX - 1.
 4:	fsubl	MO(one)		// x-1 : x : log(2)
-	fld	%st		// x-1 : x-1 : x : log(2)
+6:	fld	%st		// x-1 : x-1 : x : log(2)
 	fabs			// |x-1| : x-1 : x : log(2)
 	fcompl	MO(limit)	// x-1 : x : log(2)
 	fnstsw			// x-1 : x : log(2)
diff --git a/sysdeps/i386/i686/fpu/e_logl.S b/sysdeps/i386/i686/fpu/e_logl.S
index a0d1107..0ccc8fc 100644
--- a/sysdeps/i386/i686/fpu/e_logl.S
+++ b/sysdeps/i386/i686/fpu/e_logl.S
@@ -39,8 +39,11 @@ ENTRY(__ieee754_logl)
 	LOAD_PIC_REG (dx)
 #endif
 	fld	%st		// x : x : log(2)
+	movzwl	4+8(%esp), %eax
+	cmpl	$0xc000, %eax
+	jae	5f		// x <= -2, avoid overflow from -LDBL_MAX - 1.
 	fsubl	MO(one)		// x-1 : x : log(2)
-	fld	%st		// x-1 : x-1 : x : log(2)
+5:	fld	%st		// x-1 : x-1 : x : log(2)
 	fabs			// |x-1| : x-1 : x : log(2)
 	fld	MO(limit)	// 0.29 : |x-1| : x-1 : x : log(2)
 	fcomip	%st(1)		// |x-1| : x-1 : x : log(2)
diff --git a/sysdeps/x86_64/fpu/e_logl.S b/sysdeps/x86_64/fpu/e_logl.S
index 315afc0..047b8db 100644
--- a/sysdeps/x86_64/fpu/e_logl.S
+++ b/sysdeps/x86_64/fpu/e_logl.S
@@ -38,8 +38,11 @@ ENTRY(__ieee754_logl)
 	fld	%st		// x : x : log(2)
 	testb	$1, %ah
 	jnz	3f		// in case x is NaN or +-Inf
+	movzwl	8+8(%rsp), %eax
+	cmpl	$0xc000, %eax
+	jae	6f		// x <= -2, avoid overflow from -LDBL_MAX - 1.
 4:	fsubl	MO(one)		// x-1 : x : log(2)
-	fld	%st		// x-1 : x-1 : x : log(2)
+6:	fld	%st		// x-1 : x-1 : x : log(2)
 	fabs			// |x-1| : x-1 : x : log(2)
 	fcompl	MO(limit)	// x-1 : x : log(2)
 	fnstsw			// x-1 : x : log(2)