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2d3b0a687b
patch to fix half-cycle trigonometric functions
Paul Zimmermann, a MPFR developer, contacted me about large errors in
the half-cycle trigonometric functions. I've have investigated these
issues and developed the attached patch. The float, double, and ld80
(long double) changes have been tested.
Caveat emptor: The ld128 changes have not been compiled. The ld128
changes have not been tested. I do not have access to a system that
uses ld128 floating point.
Here is an itemized list of changes:
* lib/msun/src/math_private.h:
. Add fast floor macros to compute the integer part of |x| for
0 <= |x| 01xp(N-1), where N is the precision of the type of x.
These macros are used in the half-cycle trigonometric functions
(e.g., sinpi(x)).
. The FFLOOR80 macros is used with the Intel 80-bit extended double
functions. This macors corrects an off-by-one error, which led to
enormous error for |x| > 0x1p32.
* lib/msun/src/s_cospif.c:
* lib/msun/src/s_cospi.c:
* lib/msun/ld80/s_cospil.c:
. Update Copyright years.
. Use FFLOOR*() macro to get integer part of |x|.
. Correct handle the range 0x1p(N-1) <= |x| < 0x1pN. Here, one needs
to determine if the integral value of |x| is even or odd to choose
+1 or -1. If |x| >= 0x1pN, always return +1.
* lib/msun/src/s_sinpif.c:
* lib/msun/src/s_sinpi.c:
* lib/msun/ld80/s_sinpil.c:
. Update Copyright years.
. Use FFLOOR*() macro to get integer part of |x|.
* lib/msun/src/s_tanpif.c:
* lib/msun/src/s_tanpi.c:
* lib/msun/ld80/s_tanpil.c:
. Update Copyright years.
. For +-0.5, return +-inf. Previously, tanpi[fl]() returned an NaN.
. Use FFLOOR*() to get integer part of |x|. Need to determine if the
integer part is even or odd. This is used to set +-0 for |x|
integral
and +-inf for (n+1/2).
. For 0x1p(N-1) <= |x| < 0x1pN need to determine if x is an even or
odd
integer to select +0 or -0. For |x| >= 0x1pN, it is always an even
integer, select 0.
. Note, tanpi[fl](x) is an odd function, so one needs to consider
tanpi[fl](-|x|) = - tanpi[fl](|x|).
* lib/msun/ld128/s_cospil.c:
* lib/msun/ld128/s_sinpil.c:
* lib/msun/ld128/s_tanpil.c:
. Update Copyright years.
. These routines use an FFLOOR128 macros, which likely should be
replaced by a bit twiddling algorithm.
. The same considerations above are applied to 0x1p112 <= |x| <
0x1p113,
and |x| >= 0x1p113 cases.
. Note, even and odd determination used fmodl(x,2.), which is likely
slow.
PR: 272742
MFC after: 1 week
109 lines
2.9 KiB
C
109 lines
2.9 KiB
C
/*-
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* Copyright (c) 2017-2023 Steven G. Kargl
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* All rights reserved.
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*
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* Redistribution and use in source and binary forms, with or without
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* modification, are permitted provided that the following conditions
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* are met:
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* 1. Redistributions of source code must retain the above copyright
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* notice unmodified, this list of conditions, and the following
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* disclaimer.
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* 2. Redistributions in binary form must reproduce the above copyright
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* notice, this list of conditions and the following disclaimer in the
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* documentation and/or other materials provided with the distribution.
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*
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* THIS SOFTWARE IS PROVIDED BY THE AUTHOR ``AS IS'' AND ANY EXPRESS OR
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* IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES
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* OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE DISCLAIMED.
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* IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR ANY DIRECT, INDIRECT,
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* INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT
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* NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
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* DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
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* THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
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* (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF
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* THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
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*/
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/*
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* See ../src/s_cospi.c for implementation details.
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*/
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#include "fpmath.h"
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#include "math.h"
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#include "math_private.h"
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/*
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* pi_hi contains the leading 56 bits of a 169 bit approximation for pi.
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*/
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static const long double
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pi_hi = 3.14159265358979322702026593105983920e+00L,
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pi_lo = 1.14423774522196636802434264184180742e-17L;
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#include "k_cospil.h"
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#include "k_sinpil.h"
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volatile static const double vzero = 0;
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long double
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cospil(long double x)
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{
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long double ai, ar, ax, c;
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ax = fabsl(x);
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if (ax <= 1) {
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if (ax < 0.25) {
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if (ax < 0x1p-60) {
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if ((int)x == 0)
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return (1);
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}
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return (__kernel_cospil(ax));
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}
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if (ax < 0.5)
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c = __kernel_sinpil(0.5 - ax);
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else if (ax < 0.75) {
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if (ax == 0.5)
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return (0);
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c = -__kernel_sinpil(ax - 0.5);
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} else
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c = -__kernel_cospil(1 - ax);
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return (c);
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}
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if (ax < 0x1p112) {
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/* Split ax = ai + ar with 0 <= ar < 1. */
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FFLOORL128(ax, ai, ar);
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if (ar < 0.5) {
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if (ar < 0.25)
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c = ar == 0 ? 1 : __kernel_cospil(ar);
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else
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c = __kernel_sinpil(0.5 - ar);
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} else {
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if (ar < 0.75) {
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if (ar == 0.5)
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return (0);
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c = -__kernel_sinpil(ar - 0.5);
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} else
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c = -__kernel_cospil(1 - ar);
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}
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return (fmodl(ai, 2.L) == 0 ? c : -c);
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}
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if (isinf(x) || isnan(x))
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return (vzero / vzero);
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/*
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* For |x| >= 0x1p113, it is always an even integer, so return 1.
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*/
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if (ax >= 0x1p113)
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return (1);
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/*
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* For 0x1p112 <= |x| < 0x1p113 need to determine if x is an even
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* or odd integer to return 1 or -1.
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*/
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return (fmodl(ax, 2.L) == 0 ? 1 : -1);
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}
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