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

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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.
This commit is contained in:
Joseph Myers 2015-04-28 17:27:02 +00:00
parent fb4041ae53
commit 7d0b257541
4 changed files with 21 additions and 2 deletions
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8
ChangeLog
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@ -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.

2
NEWS
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@ -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.

11
math/libm-test.inc
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@ -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),

2
sysdeps/ieee754/ldbl-128/s_roundl.c
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@ -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)
{