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, 14 insertions, 0 deletions

diff --git a/manual/arith.texi b/manual/arith.texi
index f90ef26c91..b0464e101e 100644
--- a/manual/arith.texi
+++ b/manual/arith.texi
@@ -1596,6 +1596,20 @@ current rounding mode).
 
 @comment math.h
 @comment ISO
+@deftypefun double roundeven (double @var{x})
+@comment math.h
+@comment ISO
+@deftypefunx float roundevenf (float @var{x})
+@comment math.h
+@comment ISO
+@deftypefunx {long double} roundevenl (long double @var{x})
+@safety{@prelim{}@mtsafe{}@assafe{}@acsafe{}}
+These functions, from TS 18661-1:2014, are similar to @code{round},
+but they round halfway cases to even instead of away from zero.
+@end deftypefun
+
+@comment math.h
+@comment ISO
 @deftypefun {long int} lrint (double @var{x})
 @comment math.h
 @comment ISO