Fix acosh (1) in round-downward mode (bug 16927).

According to C99 and C11 Annex F, acosh (1) should be +0 in all
rounding modes.  However, some implementations in glibc wrongly return
-0 in round-downward mode (which is what you get if you end up
computing log1p (-0), via 1 - 1 being -0 in round-downward mode).
This patch fixes the problem implementations, by correcting the test
for an exact 1 value in the ldbl-96 implementation to allow for the
explicit high bit of the mantissa, and by inserting fabs instructions
in the i386 implementations; tests of acosh are duly converted to
ALL_RM_TEST.  I believe all the other sysdeps/ieee754 implementations
are already OK (I haven't checked the ia64 versions, but if buggy then
that will be obvious from the results of test runs after this patch is
in).

Tested x86_64 and x86 and ulps updated accordingly.

	[BZ #16927]
	* sysdeps/i386/fpu/e_acosh.S (__ieee754_acosh): Use fabs on x-1
	value.
	* sysdeps/i386/fpu/e_acoshf.S (__ieee754_acoshf): Likewise.
	* sysdeps/i386/fpu/e_acoshl.S (__ieee754_acoshl): Likewise.
	* sysdeps/ieee754/ldbl-96/e_acoshl.c (__ieee754_acoshl): Correct
	for explicit high bit of mantissa when testing for argument equal
	to 1.
	* math/libm-test.inc (acosh_test): Use ALL_RM_TEST.
	* sysdeps/i386/fpu/libm-test-ulps: Update.
	* sysdeps/x86_64/fpu/libm-test-ulps: Likewise.

9 files changed, 45 insertions, 5 deletions

diff --git a/ChangeLog b/ChangeLog
index 62192f3b93..a4376290ad 100644
--- a/ChangeLog
+++ b/ChangeLog
@@ -1,5 +1,17 @@
 2014-05-14  Joseph Myers  <joseph@codesourcery.com>
 
+	[BZ #16927]
+	* sysdeps/i386/fpu/e_acosh.S (__ieee754_acosh): Use fabs on x-1
+	value.
+	* sysdeps/i386/fpu/e_acoshf.S (__ieee754_acoshf): Likewise.
+	* sysdeps/i386/fpu/e_acoshl.S (__ieee754_acoshl): Likewise.
+	* sysdeps/ieee754/ldbl-96/e_acoshl.c (__ieee754_acoshl): Correct
+	for explicit high bit of mantissa when testing for argument equal
+	to 1.
+	* math/libm-test.inc (acosh_test): Use ALL_RM_TEST.
+	* sysdeps/i386/fpu/libm-test-ulps: Update.
+	* sysdeps/x86_64/fpu/libm-test-ulps: Likewise.
+
 	[BZ #16516]
 	* sysdeps/ieee754/dbl-64/s_erf.c (efx8): Remove variable.
 	(__erf): Scale by 16 instead of 8 in potentially underflowing
diff --git a/NEWS b/NEWS
index 9293f802f8..974d2c80a9 100644
--- a/NEWS
+++ b/NEWS
@@ -17,7 +17,7 @@ Version 2.20
   16713, 16714, 16731, 16739, 16740, 16743, 16754, 16758, 16759, 16760,
   16770, 16786, 16789, 16791, 16799, 16800, 16815, 16823, 16824, 16831,
   16838, 16854, 16876, 16877, 16885, 16888, 16890, 16912, 16916, 16922,
-  16932.
+  16927, 16932.
 
 * 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 a4bf0b88c3..b4177e8f8e 100644
--- a/math/libm-test.inc
+++ b/math/libm-test.inc
@@ -1792,9 +1792,7 @@ static const struct test_f_f_data acosh_test_data[] =
 static void
 acosh_test (void)
 {
-  START (acosh, 0);
-  RUN_TEST_LOOP_f_f (acosh, acosh_test_data, );
-  END;
+  ALL_RM_TEST (acosh, 0, acosh_test_data, RUN_TEST_LOOP_f_f, END);
 }
 
 static const struct test_f_f_data asin_test_data[] =
diff --git a/sysdeps/i386/fpu/e_acosh.S b/sysdeps/i386/fpu/e_acosh.S
index 98a329179b..c66781c985 100644
--- a/sysdeps/i386/fpu/e_acosh.S
+++ b/sysdeps/i386/fpu/e_acosh.S
@@ -52,6 +52,7 @@ ENTRY(__ieee754_acosh)
 
 	// 1 <= x <= 2 => y = log1p(x-1+sqrt(2*(x-1)+(x-1)^2))
 	fsubl	MO(one)			// x-1 : log(2)
+	fabs				// acosh(1) is +0 in all rounding modes
 	fld	%st			// x-1 : x-1 : log(2)
 	fmul	%st(1)			// (x-1)^2 : x-1 : log(2)
 	fadd	%st(1)			// x-1+(x-1)^2 : x-1 : log(2)
diff --git a/sysdeps/i386/fpu/e_acoshf.S b/sysdeps/i386/fpu/e_acoshf.S
index db9cf337b2..fa35d50fd0 100644
--- a/sysdeps/i386/fpu/e_acoshf.S
+++ b/sysdeps/i386/fpu/e_acoshf.S
@@ -52,6 +52,7 @@ ENTRY(__ieee754_acoshf)
 
 	// 1 <= x <= 2 => y = log1p(x-1+sqrt(2*(x-1)+(x-1)^2))
 	fsubl	MO(one)			// x-1 : log(2)
+	fabs				// acosh(1) is +0 in all rounding modes
 	fld	%st			// x-1 : x-1 : log(2)
 	fmul	%st(1)			// (x-1)^2 : x-1 : log(2)
 	fadd	%st(1)			// x-1+(x-1)^2 : x-1 : log(2)
diff --git a/sysdeps/i386/fpu/e_acoshl.S b/sysdeps/i386/fpu/e_acoshl.S
index a832155d17..38d8110550 100644
--- a/sysdeps/i386/fpu/e_acoshl.S
+++ b/sysdeps/i386/fpu/e_acoshl.S
@@ -59,6 +59,7 @@ ENTRY(__ieee754_acoshl)
 
 	// 1 <= x <= 2 => y = log1p(x-1+sqrt(2*(x-1)+(x-1)^2))
 	fsubl	MO(one)			// x-1 : log(2)
+	fabs				// acosh(1) is +0 in all rounding modes
 	fld	%st			// x-1 : x-1 : log(2)
 	fmul	%st(1)			// (x-1)^2 : x-1 : log(2)
 	fadd	%st(1)			// x-1+(x-1)^2 : x-1 : log(2)
diff --git a/sysdeps/i386/fpu/libm-test-ulps b/sysdeps/i386/fpu/libm-test-ulps
index aea6c51b23..ccef44ac63 100644
--- a/sysdeps/i386/fpu/libm-test-ulps
+++ b/sysdeps/i386/fpu/libm-test-ulps
@@ -21,6 +21,18 @@ Function: "acos_upward":
 ildouble: 1
 ldouble: 1
 
+Function: "acosh_downward":
+ildouble: 2
+ldouble: 2
+
+Function: "acosh_towardzero":
+ildouble: 2
+ldouble: 2
+
+Function: "acosh_upward":
+ildouble: 1
+ldouble: 1
+
 Function: "asin_downward":
 double: 1
 float: 1
diff --git a/sysdeps/ieee754/ldbl-96/e_acoshl.c b/sysdeps/ieee754/ldbl-96/e_acoshl.c
index bbaef680bd..cf9a6db0ef 100644
--- a/sysdeps/ieee754/ldbl-96/e_acoshl.c
+++ b/sysdeps/ieee754/ldbl-96/e_acoshl.c
@@ -48,7 +48,7 @@ __ieee754_acoshl(long double x)
 		return x+x;
 	    } else
 		return __ieee754_logl(x)+ln2;	/* acoshl(huge)=logl(2x) */
-	} else if(((se-0x3fff)|i0|i1)==0) {
+	} else if(((se-0x3fff)|(i0^0x80000000)|i1)==0) {
 	    return 0.0;			/* acosh(1) = 0 */
 	} else if (se > 0x4000) {	/* 2**28 > x > 2 */
 	    t=x*x;
diff --git a/sysdeps/x86_64/fpu/libm-test-ulps b/sysdeps/x86_64/fpu/libm-test-ulps
index 4ba83a46fd..ad8ae9ce5c 100644
--- a/sysdeps/x86_64/fpu/libm-test-ulps
+++ b/sysdeps/x86_64/fpu/libm-test-ulps
@@ -31,6 +31,21 @@ Function: "acosh":
 double: 1
 idouble: 1
 
+Function: "acosh_downward":
+float: 1
+ildouble: 1
+ldouble: 2
+
+Function: "acosh_towardzero":
+float: 1
+ildouble: 1
+ldouble: 2
+
+Function: "acosh_upward":
+double: 1
+ildouble: 1
+ldouble: 1
+
 Function: "asin_downward":
 double: 1
 float: 1