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path: root/src/math/cos.c
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 ```1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 61 62 63 64 65 66 67 68 69 70 71 72 73 74 75 76 77 ``` ``````/* origin: FreeBSD /usr/src/lib/msun/src/s_cos.c */ /* * ==================================================== * Copyright (C) 1993 by Sun Microsystems, Inc. All rights reserved. * * Developed at SunPro, a Sun Microsystems, Inc. business. * Permission to use, copy, modify, and distribute this * software is freely granted, provided that this notice * is preserved. * ==================================================== */ /* cos(x) * Return cosine function of x. * * kernel function: * __sin ... sine function on [-pi/4,pi/4] * __cos ... cosine function on [-pi/4,pi/4] * __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 "libm.h" double cos(double x) { double y[2]; uint32_t ix; unsigned n; GET_HIGH_WORD(ix, x); ix &= 0x7fffffff; /* |x| ~< pi/4 */ if (ix <= 0x3fe921fb) { if (ix < 0x3e46a09e) { /* |x| < 2**-27 * sqrt(2) */ /* raise inexact if x!=0 */ FORCE_EVAL(x + 0x1p120f); return 1.0; } return __cos(x, 0); } /* cos(Inf or NaN) is NaN */ if (ix >= 0x7ff00000) return x-x; /* argument reduction */ n = __rem_pio2(x, y); switch (n&3) { case 0: return __cos(y[0], y[1]); case 1: return -__sin(y[0], y[1], 1); case 2: return -__cos(y[0], y[1]); default: return __sin(y[0], y[1], 1); } } ``````