Refactor x86_64 libm code forcing underflow exceptions.

This patch refactors code in sysdeps/x86_64/fpu that forces underflow
exceptions and closely follows corresponding i386 code to use common
macros in x86_64-math-asm.h for that purpose.  This is mainly about
keeping the code similar to the i386 code as far as possible, since
each macro apart from DEFINE_LDBL_MIN ends up used only once.  It
would be possible to do a further refactoring to share these macros
between i386 and x86_64 (with i386 using the fcomip / fucomip versions
when building for i686 and above), but I have no immediate plans to do
so.

Tested for x86_64.

	* sysdeps/x86_64/fpu/x86_64-math-asm.h: New file.
	* sysdeps/x86_64/fpu/e_exp2l.S: Include <x86_64-math-asm.h>.
	(ldbl_min): Replace with use of DEFINE_LDBL_MIN.
	(__ieee754_exp2l): Use LDBL_CHECK_FORCE_UFLOW_NONNEG_NAN.
	* sysdeps/x86_64/fpu/e_expl.S: Include <x86_64-math-asm.h>.
	[!USE_AS_EXPM1L] (cmin): Replace with use of DEFINE_LDBL_MIN.
	(IEEE754_EXPL): Use LDBL_CHECK_FORCE_UFLOW_NONNEG.

1 files changed, 61 insertions, 0 deletions

diff --git a/sysdeps/x86_64/fpu/x86_64-math-asm.h b/sysdeps/x86_64/fpu/x86_64-math-asm.h
new file mode 100644
index 0000000000..07eecf7079
--- /dev/null
+++ b/sysdeps/x86_64/fpu/x86_64-math-asm.h
@@ -0,0 +1,61 @@
+/* Helper macros for x86_64 libm functions.
+   Copyright (C) 2015 Free Software Foundation, Inc.
+   This file is part of the GNU C Library.
+
+   The GNU C Library is free software; you can redistribute it and/or
+   modify it under the terms of the GNU Lesser General Public
+   License as published by the Free Software Foundation; either
+   version 2.1 of the License, or (at your option) any later version.
+
+   The GNU C Library is distributed in the hope that it will be useful,
+   but WITHOUT ANY WARRANTY; without even the implied warranty of
+   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
+   Lesser General Public License for more details.
+
+   You should have received a copy of the GNU Lesser General Public
+   License along with the GNU C Library; if not, see
+   <http://www.gnu.org/licenses/>.  */
+
+#ifndef _X86_64_MATH_ASM_H
+#define _X86_64_MATH_ASM_H 1
+
+/* Define constants for the minimum value of a floating-point
+   type.  */
+#define DEFINE_LDBL_MIN					\
+	.section .rodata.cst16,"aM",@progbits,16;	\
+	.p2align 4;					\
+	.type ldbl_min,@object;				\
+ldbl_min:						\
+	.byte 0, 0, 0, 0, 0, 0, 0, 0x80, 0x1, 0;	\
+	.byte 0, 0, 0, 0, 0, 0;				\
+	.size ldbl_min, .-ldbl_min;
+
+/* Force an underflow exception if the given value (nonnegative or
+   NaN) is subnormal.  The relevant constant for the minimum of the
+   type must have been defined, the MO macro must have been defined
+   for access to memory operands, and, if PIC, the PIC register must
+   have been loaded.  */
+#define LDBL_CHECK_FORCE_UFLOW_NONNEG_NAN	\
+	fldt	MO(ldbl_min);			\
+	fld	%st(1);				\
+	fucomip	%st(1), %st(0);			\
+	fstp	%st(0);				\
+	jnc 6464f;				\
+	fld	%st(0);				\
+	fmul	%st(0);				\
+	fstp	%st(0);				\
+6464:
+
+/* Likewise, but the argument is nonnegative and not a NaN.  */
+#define LDBL_CHECK_FORCE_UFLOW_NONNEG		\
+	fldt	MO(ldbl_min);			\
+	fld	%st(1);				\
+	fcomip	%st(1), %st(0);			\
+	fstp	%st(0);				\
+	jnc 6464f;				\
+	fld	%st(0);				\
+	fmul	%st(0);				\
+	fstp	%st(0);				\
+6464:
+
+#endif /* x86_64-math-asm.h.  */