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7d0b257541
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.
94 lines
2.1 KiB
C
94 lines
2.1 KiB
C
/* Round long double to integer away from zero.
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Copyright (C) 1997-2015 Free Software Foundation, Inc.
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This file is part of the GNU C Library.
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Contributed by Ulrich Drepper <drepper@cygnus.com>, 1997 and
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Jakub Jelinek <jj@ultra.linux.cz>, 1999.
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The GNU C Library is free software; you can redistribute it and/or
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modify it under the terms of the GNU Lesser General Public
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License as published by the Free Software Foundation; either
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version 2.1 of the License, or (at your option) any later version.
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The GNU C Library is distributed in the hope that it will be useful,
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but WITHOUT ANY WARRANTY; without even the implied warranty of
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MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
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Lesser General Public License for more details.
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You should have received a copy of the GNU Lesser General Public
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License along with the GNU C Library; if not, see
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<http://www.gnu.org/licenses/>. */
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#include <math.h>
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#include <math_private.h>
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static const long double huge = 1.0E4930L;
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long double
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__roundl (long double x)
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{
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int32_t j0;
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u_int64_t i1, i0;
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GET_LDOUBLE_WORDS64 (i0, i1, x);
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j0 = ((i0 >> 48) & 0x7fff) - 0x3fff;
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if (j0 < 48)
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{
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if (j0 < 0)
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{
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if (huge + x > 0.0)
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{
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i0 &= 0x8000000000000000ULL;
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if (j0 == -1)
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i0 |= 0x3fff000000000000LL;
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i1 = 0;
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}
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}
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else
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{
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u_int64_t i = 0x0000ffffffffffffLL >> j0;
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if (((i0 & i) | i1) == 0)
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/* X is integral. */
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return x;
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if (huge + x > 0.0)
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{
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/* Raise inexact if x != 0. */
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i0 += 0x0000800000000000LL >> j0;
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i0 &= ~i;
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i1 = 0;
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}
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}
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}
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else if (j0 > 111)
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{
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if (j0 == 0x4000)
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/* Inf or NaN. */
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return x + x;
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else
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return x;
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}
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else
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{
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u_int64_t i = -1ULL >> (j0 - 48);
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if ((i1 & i) == 0)
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/* X is integral. */
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return x;
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if (huge + x > 0.0)
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{
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/* Raise inexact if x != 0. */
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u_int64_t j = i1 + (1LL << (111 - j0));
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if (j < i1)
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i0 += 1;
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i1 = j;
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}
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i1 &= ~i;
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}
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SET_LDOUBLE_WORDS64 (x, i0, i1);
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return x;
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}
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weak_alias (__roundl, roundl)
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