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.

1 files changed, 4 insertions, 1 deletions

diff --git a/sysdeps/i386/fpu/e_logl.S b/sysdeps/i386/fpu/e_logl.S
index edae1d70df..828e98aa8d 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)