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dfa0f62011
The ldbl-128ibm implementation of nearbyintl wrongly uses signaling comparisons such as "if (fabs (u.d[0].d) < TWO52)" on arguments that might be NaNs, when "invalid" exceptions should not be raised. (For hard float, this issue may be hidden by <https://gcc.gnu.org/bugzilla/show_bug.cgi?id=58684>, powerpc GCC wrongly only using unordered comparison instructions.) This patch fixes this by just returning the argument if it is not finite (because of the arbitrary value of the low part of a NaN in IBM long double, there are quite a lot of comparisons that could end up involving a NaN when the argument to nearbyintl is a NaN, so excluding NaN arguments at the start is the simplest and safest fix). Tested for powerpc-nofpu, where it removes failures for spurious "invalid" exceptions from nearbyintl. [BZ #18857] * sysdeps/ieee754/ldbl-128ibm/s_nearbyintl.c (__nearbyintl): Just return non-finite argument without doing ordered comparisons on it.
127 lines
3.5 KiB
C
127 lines
3.5 KiB
C
/* Round to int long double floating-point values without raising inexact.
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IBM extended format long double version.
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Copyright (C) 2006-2015 Free Software Foundation, Inc.
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This file is part of the GNU C Library.
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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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/* This has been coded in assembler because GCC makes such a mess of it
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when it's coded in C. */
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#include <math.h>
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#include <math_private.h>
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#include <fenv.h>
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#include <math_ldbl_opt.h>
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#include <float.h>
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#include <ieee754.h>
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long double
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__nearbyintl (long double x)
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{
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fenv_t env;
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static const long double TWO52 = 4503599627370496.0L;
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union ibm_extended_long_double u;
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u.ld = x;
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if (!isfinite (u.d[0].d))
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return x;
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else if (fabs (u.d[0].d) < TWO52)
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{
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double xh = u.d[0].d;
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double high = u.d[0].d;
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feholdexcept (&env);
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if (high > 0.0)
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{
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high += TWO52;
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high -= TWO52;
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if (high == -0.0) high = 0.0;
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}
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else if (high < 0.0)
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{
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high -= TWO52;
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high += TWO52;
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if (high == 0.0) high = -0.0;
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}
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if (u.d[1].d > 0.0 && (xh - high == 0.5))
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high += 1.0;
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else if (u.d[1].d < 0.0 && (-(xh - high) == 0.5))
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high -= 1.0;
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u.d[0].d = high;
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u.d[1].d = 0.0;
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math_force_eval (u.d[0]);
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math_force_eval (u.d[1]);
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fesetenv (&env);
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}
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else if (fabs (u.d[1].d) < TWO52 && u.d[1].d != 0.0)
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{
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double high = u.d[0].d, low = u.d[1].d, tau;
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/* In this case we have to round the low double and handle any
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adjustment to the high double that may be caused by rounding
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(up). This is complicated by the fact that the high double
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may already be rounded and the low double may have the
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opposite sign to compensate. */
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feholdexcept (&env);
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if (u.d[0].d > 0.0)
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{
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if (u.d[1].d > 0.0)
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{
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/* If the high/low doubles are the same sign then simply
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round the low double. */
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}
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else if (u.d[1].d < 0.0)
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{
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/* Else the high double is pre rounded and we need to
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adjust for that. */
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tau = __nextafter (u.d[0].d, 0.0);
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tau = (u.d[0].d - tau) * 2.0;
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high -= tau;
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low += tau;
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}
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low += TWO52;
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low -= TWO52;
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}
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else if (u.d[0].d < 0.0)
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{
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if (u.d[1].d < 0.0)
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{
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/* If the high/low doubles are the same sign then simply
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round the low double. */
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}
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else if (u.d[1].d > 0.0)
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{
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/* Else the high double is pre rounded and we need to
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adjust for that. */
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tau = __nextafter (u.d[0].d, 0.0);
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tau = (u.d[0].d - tau) * 2.0;
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high -= tau;
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low += tau;
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}
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low = TWO52 - low;
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low = -(low - TWO52);
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}
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u.d[0].d = high + low;
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u.d[1].d = high - u.d[0].d + low;
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math_force_eval (u.d[0]);
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math_force_eval (u.d[1]);
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fesetenv (&env);
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}
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return u.ld;
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}
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long_double_symbol (libm, __nearbyintl, nearbyintl);
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