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, 102 insertions, 0 deletions

diff --git a/sysdeps/ieee754/ldbl-128/s_roundevenl.c b/sysdeps/ieee754/ldbl-128/s_roundevenl.c
new file mode 100644
index 0000000..de042ac
--- /dev/null
+++ b/sysdeps/ieee754/ldbl-128/s_roundevenl.c
@@ -0,0 +1,102 @@
+/* Round to nearest integer value, rounding halfway cases to even.
+   ldbl-128 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>
+#include <stdint.h>
+
+#define BIAS 0x3fff
+#define MANT_DIG 113
+#define MAX_EXP (2 * BIAS + 1)
+
+_Float128
+roundevenl (_Float128 x)
+{
+  uint64_t hx, lx, uhx;
+  GET_LDOUBLE_WORDS64 (hx, lx, x);
+  uhx = hx & 0x7fffffffffffffffULL;
+  int exponent = uhx >> (MANT_DIG - 1 - 64);
+  if (exponent >= BIAS + MANT_DIG - 1)
+    {
+      /* Integer, infinity or NaN.  */
+      if (exponent == MAX_EXP)
+	/* Infinity or NaN; quiet signaling NaNs.  */
+	return x + x;
+      else
+	return x;
+    }
+  else if (exponent >= BIAS + MANT_DIG - 64)
+    {
+      /* Not necessarily an integer; integer bit is in low word.
+	 Locate the bits with exponents 0 and -1.  */
+      int int_pos = (BIAS + MANT_DIG - 1) - exponent;
+      int half_pos = int_pos - 1;
+      uint64_t half_bit = 1ULL << half_pos;
+      uint64_t int_bit = 1ULL << int_pos;
+      if ((lx & (int_bit | (half_bit - 1))) != 0)
+	{
+	  /* Carry into the exponent works correctly.  No need to test
+	     whether HALF_BIT is set.  */
+	  lx += half_bit;
+	  hx += lx < half_bit;
+	}
+      lx &= ~(int_bit - 1);
+    }
+  else if (exponent == BIAS + MANT_DIG - 65)
+    {
+      /* Not necessarily an integer; integer bit is bottom of high
+	 word, half bit is top of low word.  */
+      if (((hx & 1) | (lx & 0x7fffffffffffffffULL)) != 0)
+	{
+	  lx += 0x8000000000000000ULL;
+	  hx += lx < 0x8000000000000000ULL;
+	}
+      lx = 0;
+    }
+  else if (exponent >= BIAS)
+    {
+      /* At least 1; not necessarily an integer, integer bit and half
+	 bit are in the high word.  Locate the bits with exponents 0
+	 and -1 (when the unbiased exponent is 0, the bit with
+	 exponent 0 is implicit, but as the bias is odd it is OK to
+	 take it from the low bit of the exponent).  */
+      int int_pos = (BIAS + MANT_DIG - 65) - exponent;
+      int half_pos = int_pos - 1;
+      uint64_t half_bit = 1ULL << half_pos;
+      uint64_t int_bit = 1ULL << int_pos;
+      if (((hx & (int_bit | (half_bit - 1))) | lx) != 0)
+	hx += half_bit;
+      hx &= ~(int_bit - 1);
+      lx = 0;
+    }
+  else if (exponent == BIAS - 1 && (uhx > 0x3ffe000000000000ULL || lx != 0))
+    {
+      /* Interval (0.5, 1).  */
+      hx = (hx & 0x8000000000000000ULL) | 0x3fff000000000000ULL;
+      lx = 0;
+    }
+  else
+    {
+      /* Rounds to 0.  */
+      hx &= 0x8000000000000000ULL;
+      lx = 0;
+    }
+  SET_LDOUBLE_WORDS64 (x, hx, lx);
+  return x;
+}