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-rw-r--r--ChangeLog4
-rw-r--r--math/libm-test.inc3
-rw-r--r--sysdeps/i386/fpu/s_fdim.c50
3 files changed, 57 insertions, 0 deletions
diff --git a/ChangeLog b/ChangeLog
index b6d20dc89d..a4a1cea4ab 100644
--- a/ChangeLog
+++ b/ChangeLog
@@ -1,5 +1,9 @@
 2016-06-14  Joseph Myers  <joseph@codesourcery.com>
 
+	[BZ #20255]
+	* sysdeps/i386/fpu/s_fdim.c: New file.  Based on math/s_fdim.c.
+	* math/libm-test.inc (fdim_test_data): Add another test.
+
 	[BZ #6796]
 	[BZ #20255]
 	[BZ #20256]
diff --git a/math/libm-test.inc b/math/libm-test.inc
index cc41c63e7a..d6cad6634c 100644
--- a/math/libm-test.inc
+++ b/math/libm-test.inc
@@ -7203,6 +7203,9 @@ static const struct test_ff_f_data fdim_test_data[] =
     TEST_ff_f (fdim, 0, 9, 0, NO_INEXACT_EXCEPTION|ERRNO_UNCHANGED),
     TEST_ff_f (fdim, -9, 0, 0, NO_INEXACT_EXCEPTION|ERRNO_UNCHANGED),
     TEST_ff_f (fdim, 0, -9, 9, NO_INEXACT_EXCEPTION|ERRNO_UNCHANGED),
+#if TEST_COND_binary64
+    TEST_ff_f (fdim, 1.0, -0x1.0000000000001p-53, 1.0, INEXACT_EXCEPTION|ERRNO_UNCHANGED, 0x1.0000000000001p0, INEXACT_EXCEPTION|ERRNO_UNCHANGED, 1.0, INEXACT_EXCEPTION|ERRNO_UNCHANGED, 0x1.0000000000001p0, INEXACT_EXCEPTION|ERRNO_UNCHANGED),
+#endif
     TEST_ff_f (fdim, min_subnorm_value, min_subnorm_value, 0, NO_INEXACT_EXCEPTION|ERRNO_UNCHANGED),
     TEST_ff_f (fdim, -min_subnorm_value, -min_subnorm_value, 0, NO_INEXACT_EXCEPTION|ERRNO_UNCHANGED),
     TEST_ff_f (fdim, min_subnorm_value, -min_subnorm_value, 2*min_subnorm_value, NO_INEXACT_EXCEPTION|ERRNO_UNCHANGED),
diff --git a/sysdeps/i386/fpu/s_fdim.c b/sysdeps/i386/fpu/s_fdim.c
new file mode 100644
index 0000000000..e4db9bf66c
--- /dev/null
+++ b/sysdeps/i386/fpu/s_fdim.c
@@ -0,0 +1,50 @@
+/* Return positive difference between arguments.  i386 version.
+   Copyright (C) 1997-2016 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/>.  */
+
+#include <errno.h>
+#include <fpu_control.h>
+#include <math.h>
+#include <math_private.h>
+
+double
+__fdim (double x, double y)
+{
+  if (islessequal (x, y))
+    return 0.0;
+
+  /* To avoid double rounding, set double precision for the
+     subtraction.  math_narrow_eval is still needed to eliminate
+     excess range in the case of overflow.  If the result of the
+     subtraction is in the subnormal range for double, it is exact, so
+     no issues of double rounding for subnormals arise.  */
+  fpu_control_t cw, cw_double;
+  _FPU_GETCW (cw);
+  cw_double = (cw & ~_FPU_EXTENDED) | _FPU_DOUBLE;
+  _FPU_SETCW (cw_double);
+  double r = math_narrow_eval (x - y);
+  _FPU_SETCW (cw);
+  if (isinf (r) && !isinf (x) && !isinf (y))
+    __set_errno (ERANGE);
+
+  return r;
+}
+weak_alias (__fdim, fdim)
+#ifdef NO_LONG_DOUBLE
+strong_alias (__fdim, __fdiml)
+weak_alias (__fdim, fdiml)
+#endif