Fix x86/x86_64 expm1 inaccuracy near 0 in directed rounding modes (bug 16293).

Bug 16293 is inaccuracy of x86/x86_64 versions of expm1, near 0 in
directed rounding modes, that arises from frndint rounding the
exponent to 1 or -1 instead of 0, resulting in large cancellation
error.  This inaccuracy in turn affects other functions such as sinh
that use expm1.  This patch fixes the problem by setting
round-to-nearest mode temporarily around the affected calls to
frndint.  I don't think this is needed for other uses of frndint, such
as in exp itself, as only for expm1 is the cancellation error
significant.

Tested x86_64 and x86 and ulps updated accordingly.

	* sysdeps/i386/fpu/e_expl.S (IEEE754_EXPL) [USE_AS_EXPM1L]: Set
	round-to-nearest mode when using frndint.
	* sysdeps/i386/fpu/s_expm1.S (__expm1): Likewise.
	* sysdeps/i386/fpu/s_expm1f.S (__expm1f): Likewise.
	* sysdeps/x86_64/fpu/e_expl.S (IEEE754_EXPL) [USE_AS_EXPM1L]:
	Likewise.
	* math/auto-libm-test-in: Add more tests of expm1.  Do not expect
	sinh test to fail.
	* math/auto-libm-test-out: Regenerated.
	* math/libm-test.inc (TEST_COND_x86_64): Remove macro.
	(TEST_COND_x86): Likewise.
	(expm1_tonearest_test_data): New array.
	(expm1_test_tonearest): New function.
	(expm1_towardzero_test_data): New array.
	(expm1_test_towardzero): New function.
	(expm1_downward_test_data): New array.
	(expm1_test_downward): New function.
	(expm1_upward_test_data): New array.
	(expm1_test_upward): New function.
	(main): Run the new test functions.
	* sysdeps/i386/fpu/libm-test-ulps: Update.
	* sysdeps/x86_64/fpu/libm-test-ulps: Likewise.

1 files changed, 17 insertions, 2 deletions

diff --git a/math/auto-libm-test-in b/math/auto-libm-test-in
index 50e0e6b628..28e9d455b6 100644
--- a/math/auto-libm-test-in
+++ b/math/auto-libm-test-in
@@ -281,6 +281,22 @@ expm1 -100000.0
 expm1 100000.0
 expm1 max
 expm1 -max
+expm1 0x1p-2
+expm1 -0x1p-2
+expm1 0x1p-10
+expm1 -0x1p-10
+expm1 0x1p-20
+expm1 -0x1p-20
+expm1 0x1p-29
+expm1 -0x1p-29
+expm1 0x1p-32
+expm1 -0x1p-32
+expm1 0x1p-50
+expm1 -0x1p-50
+expm1 0x1p-64
+expm1 -0x1p-64
+expm1 0x1p-100
+expm1 -0x1p-100
 
 hypot 0 0
 hypot 0 -0
@@ -835,8 +851,7 @@ sin 10
 sinh 0
 sinh -0
 sinh 0.75
-# Bug 16293: expm1 inaccurate in directed rounding modes.
-sinh 0x8p-32 xfail:x86_64:ldbl-96-intel xfail:x86
+sinh 0x8p-32
 sinh 22
 sinh 23
 sinh 24