Fix ldbl-128 roundl for exponents in [31, 47] (bug 18346).

The implementation of roundl for ldbl-128 involves undefined behavior
for arguments with exponents from 31 to 47 inclusive, from the shift:

      u_int64_t i = -1ULL >> (j0 - 48);

For example, on mips64, this means roundl (0xffffffffffff.8p0L)
wrongly returns its argument, which is not an integer.  A condition
checking for exponents < 31 should actually be checking for exponents
< 48, and this patch makes it do so.  (That condition is for whether
the bit representing 0.5 is in the high 64-bit half of the
floating-point number.  The value 31 might have arisen from an
incorrect conversion of the ldbl-96 version to handle ldbl-128.)

This was originally reported as a GCC libquadmath bug
<https://gcc.gnu.org/bugzilla/show_bug.cgi?id=65757>.

Tested for mips64; also tested for x86_64 and x86 to make sure the new
tests pass there.

	[BZ #18346]
	* sysdeps/ieee754/ldbl-128/s_roundl.c (__roundl): Handle all
	exponents less than 48 as cases where high part of mantissa needs
	examining to determine whether argument is integral.
	* math/libm-test.inc (round_test_data): Add more tests.

1 files changed, 8 insertions, 0 deletions

diff --git a/ChangeLog b/ChangeLog
index 4b58951ab4..35106b5235 100644
--- a/ChangeLog
+++ b/ChangeLog
@@ -1,3 +1,11 @@
+2015-04-28  Joseph Myers  <joseph@codesourcery.com>
+
+	[BZ #18346]
+	* sysdeps/ieee754/ldbl-128/s_roundl.c (__roundl): Handle all
+	exponents less than 48 as cases where high part of mantissa needs
+	examining to determine whether argument is integral.
+	* math/libm-test.inc (round_test_data): Add more tests.
+
 2015-04-28  Mark Wielaard  <mjw@redhat.com>
 
 	* elf/elf.h (SHF_EXCLUDE): Use unsigned 1 for shift.