78 lines
2.1 KiB
C
78 lines
2.1 KiB
C
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/* origin: FreeBSD /usr/src/lib/msun/src/s_cos.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 SunPro, 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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/* cos(x)
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* Return cosine function of x.
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*
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* kernel function:
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* __sin ... sine function on [-pi/4,pi/4]
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* __cos ... cosine function on [-pi/4,pi/4]
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* __rem_pio2 ... argument reduction routine
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*
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* Method.
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* Let S,C and T denote the sin, cos and tan respectively on
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* [-PI/4, +PI/4]. Reduce the argument x to y1+y2 = x-k*pi/2
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* in [-pi/4 , +pi/4], and let n = k mod 4.
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* We have
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*
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* n sin(x) cos(x) tan(x)
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* ----------------------------------------------------------
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* 0 S C T
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* 1 C -S -1/T
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* 2 -S -C T
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* 3 -C S -1/T
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* ----------------------------------------------------------
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*
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* Special cases:
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* Let trig be any of sin, cos, or tan.
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* trig(+-INF) is NaN, with signals;
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* trig(NaN) is that NaN;
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*
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* Accuracy:
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* TRIG(x) returns trig(x) nearly rounded
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*/
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#include "libm.h"
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double cos(double x)
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{
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double y[2];
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uint32_t ix;
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unsigned n;
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GET_HIGH_WORD(ix, x);
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ix &= 0x7fffffff;
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/* |x| ~< pi/4 */
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if (ix <= 0x3fe921fb) {
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if (ix < 0x3e46a09e) { /* |x| < 2**-27 * sqrt(2) */
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/* raise inexact if x!=0 */
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FORCE_EVAL(x + 0x1p120f);
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return 1.0;
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}
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return __cos(x, 0);
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}
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/* cos(Inf or NaN) is NaN */
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if (ix >= 0x7ff00000)
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return x-x;
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/* argument reduction */
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n = __rem_pio2(x, y);
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switch (n&3) {
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case 0: return __cos(y[0], y[1]);
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case 1: return -__sin(y[0], y[1], 1);
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case 2: return -__cos(y[0], y[1]);
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default:
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return __sin(y[0], y[1], 1);
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}
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}
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