Add roundeven, roundevenf, roundevenl.

TS 18661-1 defines roundeven functions that round a floating-point
number to the nearest integer, in that floating-point type, with ties
rounding to even (whereas the round functions round ties away from
zero).  As with other such functions, they raise no exceptions apart
from "invalid" for signaling NaNs.  There was a previous user request
for this functionality in glibc in
<https://sourceware.org/ml/libc-help/2015-02/msg00005.html>.

This patch implements these functions for glibc.  The implementations
use integer bit-manipulation (or roundeven on the high and low parts,
in the IBM long double case).  It's possible that there may be faster
approaches on some architectures (in particular, on AArch64 the frintn
instruction should do exactly what's required); I'll leave it to
architecture maintainers or others interested to implement such
architecture-specific versions if desired.  (Where architectures have
instructions to round to nearest integer in the current rounding mode,
implementations saving and restoring the rounding mode - and dealing
with exceptions if those instructions generate "inexact" - are also
possible, though their performance depends on the cost of manipulating
exceptions / rounding mode state.)

Tested for x86_64, x86, mips64 and powerpc.

	* math/bits/mathcalls.h [__GLIBC_USE (IEC_60559_BFP_EXT)]
	(roundeven): New declaration.
	* math/tgmath.h [__GLIBC_USE (IEC_60559_BFP_EXT)] (roundeven): New
	macro.
	* math/Versions (roundeven): New libm symbol at version
	GLIBC_2.25.
	(roundevenf): Likewise.
	(roundevenl): Likewise.
	* math/Makefile (libm-calls): Add s_roundevenF.
	* math/libm-test.inc (roundeven_test_data): New array.
	(roundeven_test): New function.
	(main): Call roundeven_test.
	* math/test-tgmath.c (NCALLS): Increase to 134.
	(F(compile_test)): Call roundeven.
	(F(roundeven)): New function.
	* manual/arith.texi (Rounding Functions): Document roundeven,
	roundevenf and roundevenl.
	* manual/libm-err-tab.pl (@all_functions): Add roundeven.
	* include/math.h (roundeven): Use libm_hidden_proto.
	* sysdeps/ieee754/dbl-64/s_roundeven.c: New file.
	* sysdeps/ieee754/dbl-64/wordsize-64/s_roundeven.c: Likewise.
	* sysdeps/ieee754/flt-32/s_roundevenf.c: Likewise.
	* sysdeps/ieee754/ldbl-128/s_roundevenl.c: Likewise.
	* sysdeps/ieee754/ldbl-128ibm/s_roundevenl.c: Likewise.
	* sysdeps/ieee754/ldbl-96/s_roundevenl.c: Likewise.
	* sysdeps/ieee754/ldbl-opt/Makefile (libnldbl-calls): Add
	roundeven.
	(CFLAGS-nldbl-roundeven.c): New variable.
	* sysdeps/ieee754/ldbl-opt/nldbl-roundeven.c: New file.
	* sysdeps/nacl/libm.abilist: Update.
	* sysdeps/unix/sysv/linux/aarch64/libm.abilist: Likewise.
	* sysdeps/unix/sysv/linux/alpha/libm.abilist: Likewise.
	* sysdeps/unix/sysv/linux/arm/libm.abilist: Likewise.
	* sysdeps/unix/sysv/linux/hppa/libm.abilist: Likewise.
	* sysdeps/unix/sysv/linux/i386/libm.abilist: Likewise.
	* sysdeps/unix/sysv/linux/ia64/libm.abilist: Likewise.
	* sysdeps/unix/sysv/linux/m68k/coldfire/libm.abilist: Likewise.
	* sysdeps/unix/sysv/linux/m68k/m680x0/libm.abilist: Likewise.
	* sysdeps/unix/sysv/linux/microblaze/libm.abilist: Likewise.
	* sysdeps/unix/sysv/linux/mips/mips32/libm.abilist: Likewise.
	* sysdeps/unix/sysv/linux/mips/mips64/libm.abilist: Likewise.
	* sysdeps/unix/sysv/linux/nios2/libm.abilist: Likewise.
	* sysdeps/unix/sysv/linux/powerpc/powerpc32/fpu/libm.abilist:
	Likewise.
	* sysdeps/unix/sysv/linux/powerpc/powerpc32/nofpu/libm.abilist:
	Likewise.
	* sysdeps/unix/sysv/linux/powerpc/powerpc64/libm-le.abilist:
	Likewise.
	* sysdeps/unix/sysv/linux/powerpc/powerpc64/libm.abilist:
	Likewise.
	* sysdeps/unix/sysv/linux/s390/s390-32/libm.abilist: Likewise.
	* sysdeps/unix/sysv/linux/s390/s390-64/libm.abilist: Likewise.
	* sysdeps/unix/sysv/linux/sh/libm.abilist: Likewise.
	* sysdeps/unix/sysv/linux/sparc/sparc32/libm.abilist: Likewise.
	* sysdeps/unix/sysv/linux/sparc/sparc64/libm.abilist: Likewise.
	* sysdeps/unix/sysv/linux/tile/tilegx/tilegx32/libm.abilist:
	Likewise.
	* sysdeps/unix/sysv/linux/tile/tilegx/tilegx64/libm.abilist:
	Likewise.
	* sysdeps/unix/sysv/linux/tile/tilepro/libm.abilist: Likewise.
	* sysdeps/unix/sysv/linux/x86_64/64/libm.abilist: Likewise.
	* sysdeps/unix/sysv/linux/x86_64/x32/libm.abilist: Likewise.

1 files changed, 69 insertions, 0 deletions

diff --git a/sysdeps/ieee754/ldbl-128ibm/s_roundevenl.c b/sysdeps/ieee754/ldbl-128ibm/s_roundevenl.c
new file mode 100644
index 0000000..cd91d39
--- /dev/null
+++ b/sysdeps/ieee754/ldbl-128ibm/s_roundevenl.c
@@ -0,0 +1,69 @@
+/* Round to nearest integer value, rounding halfway cases to even.
+   ldbl-128ibm version.
+   Copyright (C) 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 <math.h>
+#include <math_private.h>
+
+long double
+roundevenl (long double x)
+{
+  double xh, xl, hi;
+
+  ldbl_unpack (x, &xh, &xl);
+
+  if (xh != 0 && isfinite (xh))
+    {
+      hi = roundeven (xh);
+      if (hi != xh)
+	{
+	  /* The high part is not an integer; the low part only
+	     affects the result if the high part is exactly half way
+	     between two integers and the low part is nonzero in the
+	     opposite direction to the rounding of the high part.  */
+	  double diff = hi - xh;
+	  if (fabs (diff) == 0.5)
+	    {
+	      if (xl < 0 && diff > 0)
+		xh = hi - 1;
+	      else if (xl > 0 && diff < 0)
+		xh = hi + 1;
+	      else
+		xh = hi;
+	    }
+	  else
+	    xh = hi;
+	  xl = 0;
+	}
+      else
+	{
+	  /* The high part is a nonzero integer.  Rounding the low
+	     part to nearest, ties round to even, is always correct,
+	     as a high part that is an odd integer together with a low
+	     part with magnitude 0.5 is not a valid long double.  */
+	  xl = roundeven (xl);
+	  xh = hi;
+	  ldbl_canonicalize_int (&xh, &xl);
+	}
+    }
+  else
+    /* Quiet signaling NaN arguments.  */
+    xh += xh;
+
+  return ldbl_pack (xh, xl);
+}