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.

diff --git a/ChangeLog b/ChangeLog
index 4b58951ab43fd88a3b1db3733775936c2141bab3..35106b5235d8678fbe01ecde31352b3ebfc7b78f 100644 (file)
--- 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.

diff --git a/NEWS b/NEWS
index 72e15f523f000259177a6d30ecdded84205b927e..fc3911dc29fcc4f79793c33341325e64e45998df 100644 (file)
--- a/NEWS
+++ b/NEWS
@@ -16,7 +16,7 @@ Version 2.22
   17967, 17969, 17978, 17987, 17991, 17996, 17998, 17999, 18019, 18020,
   18029, 18030, 18032, 18036, 18038, 18039, 18042, 18043, 18046, 18047,
   18068, 18080, 18093, 18100, 18104, 18110, 18111, 18128, 18138, 18185,
-  18197, 18206, 18210, 18211, 18247, 18287, 18333.
+  18197, 18206, 18210, 18211, 18247, 18287, 18333, 18346.
 
 * Cache information can be queried via sysconf() function on s390 e.g. with
   _SC_LEVEL1_ICACHE_SIZE as argument.

diff --git a/math/libm-test.inc b/math/libm-test.inc
index 5d7f5a25c8aa703a2944d2a8bb3a3daf58bf4c4f..4cade1492598d4ad52e837e1916725ca28c871b4 100644 (file)
--- a/math/libm-test.inc
+++ b/math/libm-test.inc
@@ -9012,6 +9012,17 @@ static const struct test_f_f_data round_test_data[] =
     TEST_f_f (round, 2097152.5, 2097153),
     TEST_f_f (round, -2097152.5, -2097153),
 
+#ifndef TEST_FLOAT
+    TEST_f_f (round, 0xffffffffffff.0p0L, 0xffffffffffff.0p0L),
+    TEST_f_f (round, 0xffffffffffff.4p0L, 0xffffffffffff.0p0L),
+    TEST_f_f (round, 0xffffffffffff.8p0L, 0x1000000000000.0p0L),
+    TEST_f_f (round, 0xffffffffffff.cp0L, 0x1000000000000.0p0L),
+    TEST_f_f (round, -0xffffffffffff.0p0L, -0xffffffffffff.0p0L),
+    TEST_f_f (round, -0xffffffffffff.4p0L, -0xffffffffffff.0p0L),
+    TEST_f_f (round, -0xffffffffffff.8p0L, -0x1000000000000.0p0L),
+    TEST_f_f (round, -0xffffffffffff.cp0L, -0x1000000000000.0p0L),
+#endif
+
 #ifdef TEST_LDOUBLE
     /* The result can only be represented in long double.  */
     TEST_f_f (round, 4503599627370495.5L, 4503599627370496.0L),

diff --git a/sysdeps/ieee754/ldbl-128/s_roundl.c b/sysdeps/ieee754/ldbl-128/s_roundl.c
index 9df0092ce859372e4f6e8f932e4e53a11162ad1c..3ff6ebe7cc00177093318862ee4c4304285cd8f9 100644 (file)
--- a/sysdeps/ieee754/ldbl-128/s_roundl.c
+++ b/sysdeps/ieee754/ldbl-128/s_roundl.c
@@ -34,7 +34,7 @@ __roundl (long double x)
 
   GET_LDOUBLE_WORDS64 (i0, i1, x);
   j0 = ((i0 >> 48) & 0x7fff) - 0x3fff;
-  if (j0 < 31)
+  if (j0 < 48)
     {
       if (j0 < 0)
        {