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 /* @(#)s_cos.c 5.1 93/09/24 */ /* * ==================================================== * 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. * ==================================================== */ #ifndef lint static char rcsid[] = "\$FreeBSD: src/lib/msun/src/s_cos.c,v 1.10 2005/10/24 14:08:36 bde Exp \$"; #endif /* 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 "math.h" #include "math_private.h" double cos(double x) { double y[2],z=0.0; int32_t n, ix; /* High word of x. */ GET_HIGH_WORD(ix,x); /* |x| ~< pi/4 */ ix &= 0x7fffffff; if(ix <= 0x3fe921fb) { if(ix<0x3e400000) /* if x < 2**-27 */ if(((int)x)==0) return 1.0; /* generate inexact */ 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); } } }