mirror of https://gitlab.com/rnger/amath
162 lines
5.2 KiB
C
162 lines
5.2 KiB
C
/*-
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* Copyright (c) 2014-2017 Carsten Sonne Larsen <cs@innolan.net>
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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, this list of conditions and the following 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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* Project homepage:
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* https://amath.innolan.net
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*
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* The original source code can be obtained from:
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* http://www.netlib.org/fdlibm/e_acos.c
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*
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* =================================================================
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* Copyright (C) 1993 by Sun Microsystems, Inc. All rights reserved.
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*
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* Developed at SunSoft, a Sun Microsystems, Inc. business.
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* Permission to use, copy, modify, and distribute this
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* software is freely granted, provided that this notice
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* is preserved.
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* =================================================================
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*/
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/**
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* @file acos.c
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* @brief Inverse cosine function
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*/
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#include "prim.h"
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static const double
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one = 1.00000000000000000000e+00, /* 0x3FF00000, 0x00000000 */
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pi = 3.14159265358979311600e+00, /* 0x400921FB, 0x54442D18 */
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pio2_hi = 1.57079632679489655800e+00, /* 0x3FF921FB, 0x54442D18 */
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pio2_lo = 6.12323399573676603587e-17, /* 0x3C91A626, 0x33145C07 */
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pS0 = 1.66666666666666657415e-01, /* 0x3FC55555, 0x55555555 */
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pS1 = -3.25565818622400915405e-01, /* 0xBFD4D612, 0x03EB6F7D */
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pS2 = 2.01212532134862925881e-01, /* 0x3FC9C155, 0x0E884455 */
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pS3 = -4.00555345006794114027e-02, /* 0xBFA48228, 0xB5688F3B */
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pS4 = 7.91534994289814532176e-04, /* 0x3F49EFE0, 0x7501B288 */
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pS5 = 3.47933107596021167570e-05, /* 0x3F023DE1, 0x0DFDF709 */
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qS1 = -2.40339491173441421878e+00, /* 0xC0033A27, 0x1C8A2D4B */
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qS2 = 2.02094576023350569471e+00, /* 0x40002AE5, 0x9C598AC8 */
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qS3 = -6.88283971605453293030e-01, /* 0xBFE6066C, 0x1B8D0159 */
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qS4 = 7.70381505559019352791e-02; /* 0x3FB3B8C5, 0xB12E9282 */
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/**
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* @brief Inverse cosine function
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* @details
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* <pre>
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* Method
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* acos(x) = pi/2 - asin(x)
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* acos(-x) = pi/2 + asin(x)
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*
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* For |x|<=0.5
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* acos(x) = pi/2 - (x + x*x^2*R(x^2)) (see asin.c)
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*
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* For x>0.5
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* acos(x) = pi/2 - (pi/2 - 2asin(sqrt((1-x)/2)))
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* = 2asin(sqrt((1-x)/2))
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* = 2s + 2s*z*R(z) ...z=(1-x)/2, s=sqrt(z)
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* = 2f + (2c + 2s*z*R(z))
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* where f=hi part of s, and c = (z-f*f)/(s+f) is the correction term
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* for f so that f+c ~ sqrt(z).
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*
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* For x<-0.5
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* acos(x) = pi - 2asin(sqrt((1-|x|)/2))
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* = pi - 0.5*(s+s*z*R(z)), where z=(1-|x|)/2,s=sqrt(z)
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*
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* Special cases
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* if x is NaN, return NaN
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* if |x|>1, return NaN
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* </pre>
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*/
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double acos(double x)
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{
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double z, p, q, r, w, s, c, df;
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int32_t hx, ix;
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uint32_t lx;
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GET_HIGH_WORD(hx, x);
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ix = hx & 0x7FFFFFFF;
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// |x| >= 1
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if (ix >= 0x3FF00000)
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{
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GET_LOW_WORD(lx, x);
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// |x|==1
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if (((ix - 0x3FF00000) | lx) == 0)
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{
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if (hx > 0)
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{
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// acos(1) = 0
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return 0.0;
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}
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// acos(-1) = pi
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return pi + 2.0 * pio2_lo;
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}
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// acos(|x|>1) is NaN
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return NAN;
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}
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// |x| < 0.5
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if (ix < 0x3FE00000)
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{
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// if |x|<2**-57
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if (ix <= 0x3C600000)
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{
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return pio2_hi + pio2_lo;
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}
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z = x * x;
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p = z * (pS0 + z * (pS1 + z * (pS2 + z * (pS3 + z * (pS4 + z * pS5)))));
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q = one + z * (qS1 + z * (qS2 + z * (qS3 + z * qS4)));
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r = p / q;
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return pio2_hi - (x - (pio2_lo - x * r));
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}
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// x < -0.5
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if (hx < 0)
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{
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z = (one + x) * 0.5;
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p = z * (pS0 + z * (pS1 + z * (pS2 + z * (pS3 + z * (pS4 + z * pS5)))));
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q = one + z * (qS1 + z * (qS2 + z * (qS3 + z * qS4)));
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s = sqrt(z);
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r = p / q;
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w = r * s - pio2_lo;
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return pi - 2.0 * (s + w);
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}
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// x > 0.5
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z = (one - x) * 0.5;
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s = sqrt(z);
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df = s;
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SET_LOW_WORD(df, 0);
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c = (z - df * df) / (s + df);
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p = z * (pS0 + z * (pS1 + z * (pS2 + z * (pS3 + z * (pS4 + z * pS5)))));
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q = one + z * (qS1 + z * (qS2 + z * (qS3 + z * qS4)));
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r = p / q;
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w = r * s + c;
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return 2.0 * (df + w);
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}
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