6f05bafeba
This patch fixes bug 16789, incorrect sign of (real part) zero result from clog and clog10 in round-downward mode, arising from that real part being computed as 0 - 0. To ensure that an underflow exception occurred, the code used an underflowing value (the next term in the series for log1p) in arithmetic computing the real part of the result, yielding the problematic 0 - 0 computation in some cases even when the mathematical result would be small but positive. The patch changes this code to use the math_force_eval approach to ensuring that an underflowing computation actually occurs. Tests of clog and clog10 are enabled in all rounding modes. Tested x86_64 and x86 and ulps updated accordingly. [BZ #16789] * math/s_clog.c (__clog): Use math_force_eval to ensure underflow instead of using underflowing value in computing result. * math/s_clog10.c (__clog10): Likewise. * math/s_clog10f.c (__clog10f): Likewise. * math/s_clog10l.c (__clog10l): Likewise. * math/s_clogf.c (__clogf): Likewise. * math/s_clogl.c (__clogl): Likewise. * math/libm-test.inc (clog_test): Use ALL_RM_TEST. (clog10_test): Likewise. * sysdeps/i386/fpu/libm-test-ulps: Update. * sysdeps/x86_64/fpu/libm-test-ulps: Likewise.
123 lines
3.4 KiB
C
123 lines
3.4 KiB
C
/* Compute complex natural logarithm.
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Copyright (C) 1997-2014 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.
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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 <complex.h>
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#include <math.h>
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#include <math_private.h>
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#include <float.h>
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__complex__ double
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__clog (__complex__ double x)
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{
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__complex__ double result;
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int rcls = fpclassify (__real__ x);
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int icls = fpclassify (__imag__ x);
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if (__glibc_unlikely (rcls == FP_ZERO && icls == FP_ZERO))
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{
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/* Real and imaginary part are 0.0. */
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__imag__ result = signbit (__real__ x) ? M_PI : 0.0;
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__imag__ result = __copysign (__imag__ result, __imag__ x);
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/* Yes, the following line raises an exception. */
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__real__ result = -1.0 / fabs (__real__ x);
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}
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else if (__glibc_likely (rcls != FP_NAN && icls != FP_NAN))
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{
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/* Neither real nor imaginary part is NaN. */
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double absx = fabs (__real__ x), absy = fabs (__imag__ x);
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int scale = 0;
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if (absx < absy)
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{
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double t = absx;
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absx = absy;
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absy = t;
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}
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if (absx > DBL_MAX / 2.0)
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{
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scale = -1;
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absx = __scalbn (absx, scale);
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absy = (absy >= DBL_MIN * 2.0 ? __scalbn (absy, scale) : 0.0);
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}
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else if (absx < DBL_MIN && absy < DBL_MIN)
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{
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scale = DBL_MANT_DIG;
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absx = __scalbn (absx, scale);
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absy = __scalbn (absy, scale);
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}
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if (absx == 1.0 && scale == 0)
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{
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double absy2 = absy * absy;
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if (absy2 <= DBL_MIN * 2.0)
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{
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double force_underflow = absy2 * absy2;
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__real__ result = absy2 / 2.0;
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math_force_eval (force_underflow);
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}
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else
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__real__ result = __log1p (absy2) / 2.0;
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}
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else if (absx > 1.0 && absx < 2.0 && absy < 1.0 && scale == 0)
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{
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double d2m1 = (absx - 1.0) * (absx + 1.0);
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if (absy >= DBL_EPSILON)
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d2m1 += absy * absy;
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__real__ result = __log1p (d2m1) / 2.0;
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}
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else if (absx < 1.0
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&& absx >= 0.75
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&& absy < DBL_EPSILON / 2.0
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&& scale == 0)
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{
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double d2m1 = (absx - 1.0) * (absx + 1.0);
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__real__ result = __log1p (d2m1) / 2.0;
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}
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else if (absx < 1.0 && (absx >= 0.75 || absy >= 0.5) && scale == 0)
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{
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double d2m1 = __x2y2m1 (absx, absy);
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__real__ result = __log1p (d2m1) / 2.0;
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}
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else
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{
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double d = __ieee754_hypot (absx, absy);
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__real__ result = __ieee754_log (d) - scale * M_LN2;
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}
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__imag__ result = __ieee754_atan2 (__imag__ x, __real__ x);
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}
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else
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{
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__imag__ result = __nan ("");
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if (rcls == FP_INFINITE || icls == FP_INFINITE)
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/* Real or imaginary part is infinite. */
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__real__ result = HUGE_VAL;
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else
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__real__ result = __nan ("");
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}
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return result;
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}
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weak_alias (__clog, clog)
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#ifdef NO_LONG_DOUBLE
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strong_alias (__clog, __clogl)
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weak_alias (__clog, clogl)
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#endif
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