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products/sources/formale Sprachen/Java/Openjdk/src/java.base/share/native/libfdlibm/ (Sun/Oracle ^©) Datei vom 13.11.2022 mit Größe 4 kB

Quelle e_asin.c Sprache: C

/*
* Copyright (c) 1998, 2001, Oracle and/or its affiliates. All rights reserved.
* DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
*
* This code is free software; you can redistribute it and/or modify it
* under the terms of the GNU General Public License version 2 only, as
* published by the Free Software Foundation.  Oracle designates this
* particular file as subject to the "Classpath" exception as provided
* by Oracle in the LICENSE file that accompanied this code.
*
* This code is distributed in the hope that it will be useful, but WITHOUT
* ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
* FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License
* version 2 for more details (a copy is included in the LICENSE file that
* accompanied this code).
*
* You should have received a copy of the GNU General Public License version
* 2 along with this work; if not, write to the Free Software Foundation,
* Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
*
* Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA
* or visit www.oracle.com if you need additional information or have any
* questions.
*/

/* __ieee754_asin(x)
* Method :
*      Since  asin(x) = x + x^3/6 + x^5*3/40 + x^7*15/336 + ...
*      we approximate asin(x) on [0,0.5] by
*              asin(x) = x + x*x^2*R(x^2)
*      where
*              R(x^2) is a rational approximation of (asin(x)-x)/x^3
*      and its remez error is bounded by
*              |(asin(x)-x)/x^3 - R(x^2)| < 2^(-58.75)
*
*      For x in [0.5,1]
*              asin(x) = pi/2-2*asin(sqrt((1-x)/2))
*      Let y = (1-x), z = y/2, s := sqrt(z), and pio2_hi+pio2_lo=pi/2;
*      then for x>0.98
*              asin(x) = pi/2 - 2*(s+s*z*R(z))
*                      = pio2_hi - (2*(s+s*z*R(z)) - pio2_lo)
*      For x<=0.98, let pio4_hi = pio2_hi/2, then
*              f = hi part of s;
*              c = sqrt(z) - f = (z-f*f)/(s+f)         ...f+c=sqrt(z)
*      and
*              asin(x) = pi/2 - 2*(s+s*z*R(z))
*                      = pio4_hi+(pio4-2s)-(2s*z*R(z)-pio2_lo)
*                      = pio4_hi+(pio4-2f)-(2s*z*R(z)-(pio2_lo+2c))
*
* Special cases:
*      if x is NaN, return x itself;
*      if |x|>1, return NaN with invalid signal.
*
*/

#include "fdlibm.h"

#ifdef __STDC__
static const double
#else
static double
#endif
one =  1.00000000000000000000e+00, /* 0x3FF00000, 0x00000000 */
huge =  1.000e+300,
pio2_hi =  1.57079632679489655800e+00, /* 0x3FF921FB, 0x54442D18 */
pio2_lo =  6.12323399573676603587e-17, /* 0x3C91A626, 0x33145C07 */
pio4_hi =  7.85398163397448278999e-01, /* 0x3FE921FB, 0x54442D18 */
        /* coefficient for R(x^2) */
pS0 =  1.66666666666666657415e-01, /* 0x3FC55555, 0x55555555 */
pS1 = -3.25565818622400915405e-01, /* 0xBFD4D612, 0x03EB6F7D */
pS2 =  2.01212532134862925881e-01, /* 0x3FC9C155, 0x0E884455 */
pS3 = -4.00555345006794114027e-02, /* 0xBFA48228, 0xB5688F3B */
pS4 =  7.91534994289814532176e-04, /* 0x3F49EFE0, 0x7501B288 */
pS5 =  3.47933107596021167570e-05, /* 0x3F023DE1, 0x0DFDF709 */
qS1 = -2.40339491173441421878e+00, /* 0xC0033A27, 0x1C8A2D4B */
qS2 =  2.02094576023350569471e+00, /* 0x40002AE5, 0x9C598AC8 */
qS3 = -6.88283971605453293030e-01, /* 0xBFE6066C, 0x1B8D0159 */
qS4 =  7.70381505559019352791e-02; /* 0x3FB3B8C5, 0xB12E9282 */

#ifdef __STDC__
        double __ieee754_asin(double x)
#else
        double __ieee754_asin(x)
        double x;
#endif
{
        double t=0,w,p,q,c,r,s;
        int hx,ix;
        hx = __HI(x);
        ix = hx&0x7fffffff;
        if(ix>= 0x3ff00000) {           /* |x|>= 1 */
            if(((ix-0x3ff00000)|__LO(x))==0)
                    /* asin(1)=+-pi/2 with inexact */
                return x*pio2_hi+x*pio2_lo;
            return (x-x)/(x-x);         /* asin(|x|>1) is NaN */
        } else if (ix<0x3fe00000) {     /* |x|<0.5 */
            if(ix<0x3e400000) {         /* if |x| < 2**-27 */
                if(huge+x>one) return x;/* return x with inexact if x!=0*/
            } else
                t = x*x;
            p = t*(pS0+t*(pS1+t*(pS2+t*(pS3+t*(pS4+t*pS5)))));
            q = one+t*(qS1+t*(qS2+t*(qS3+t*qS4)));
            w = p/q;
            return x+x*w;
        }
        /* 1> |x|>= 0.5 */
        w = one-fabs(x);
        t = w*0.5;
        p = t*(pS0+t*(pS1+t*(pS2+t*(pS3+t*(pS4+t*pS5)))));
        q = one+t*(qS1+t*(qS2+t*(qS3+t*qS4)));
        s = sqrt(t);
        if(ix>=0x3FEF3333) {    /* if |x| > 0.975 */
            w = p/q;
            t = pio2_hi-(2.0*(s+s*w)-pio2_lo);
        } else {
            w  = s;
            __LO(w) = 0;
            c  = (t-w*w)/(s+w);
            r  = p/q;
            p  = 2.0*s*r-(pio2_lo-2.0*c);
            q  = pio4_hi-2.0*w;
            t  = pio4_hi-(p-q);
        }
        if(hx>0) return t; else return -t;
}

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