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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 3 kB

Quelle s_cos.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.
*/

/* cos(x)
* Return cosine function of x.
*
* kernel function:
*      __kernel_sin            ... sine function on [-pi/4,pi/4]
*      __kernel_cos            ... cosine function on [-pi/4,pi/4]
*      __ieee754_rem_pio2      ... argument reduction routine
*
* Method.
*      Let S,C and T denote the sin, cos and tan respectively on
*      [-PI/4, +PI/4]. Reduce the argument x to y1+y2 = x-k*pi/2
*      in [-pi/4 , +pi/4], and let n = k mod 4.
*      We have
*
*          n        sin(x)      cos(x)        tan(x)
*     ----------------------------------------------------------
*          0          S           C             T
*          1          C          -S            -1/T
*          2         -S          -C             T
*          3         -C           S            -1/T
*     ----------------------------------------------------------
*
* Special cases:
*      Let trig be any of sin, cos, or tan.
*      trig(+-INF)  is NaN, with signals;
*      trig(NaN)    is that NaN;
*
* Accuracy:
*      TRIG(x) returns trig(x) nearly rounded
*/

#include "fdlibm.h"

#ifdef __STDC__
        double cos(double x)
#else
        double cos(x)
        double x;
#endif
{
        double y[2],z=0.0;
        int n, ix;

    /* High word of x. */
        ix = __HI(x);

    /* |x| ~< pi/4 */
        ix &= 0x7fffffff;
        if(ix <= 0x3fe921fb) return __kernel_cos(x,z);

    /* cos(Inf or NaN) is NaN */
        else if (ix>=0x7ff00000) return x-x;

    /* argument reduction needed */
        else {
            n = __ieee754_rem_pio2(x,y);
            switch(n&3) {
                case 0: return  __kernel_cos(y[0],y[1]);
                case 1: return -__kernel_sin(y[0],y[1],1);
                case 2: return -__kernel_cos(y[0],y[1]);
                default:
                        return  __kernel_sin(y[0],y[1],1);
            }
        }
}

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