1 2 /* @(#)s_cos.c 1.3 95/01/18 */ 3 /* 4 * ==================================================== 5 * Copyright (C) 1993 by Sun Microsystems, Inc. All rights reserved. 6 * 7 * Developed at SunSoft, a Sun Microsystems, Inc. business. 8 * Permission to use, copy, modify, and distribute this 9 * software is freely granted, provided that this notice 10 * is preserved. 11 * ==================================================== 12 */ 13 14 /* ieee_cos(x) 15 * Return cosine function of x. 16 * 17 * kernel function: 18 * __kernel_sin ... sine function on [-pi/4,pi/4] 19 * __kernel_cos ... cosine function on [-pi/4,pi/4] 20 * __ieee754_rem_pio2 ... argument reduction routine 21 * 22 * Method. 23 * Let S,C and T denote the sin, cos and tan respectively on 24 * [-PI/4, +PI/4]. Reduce the argument x to y1+y2 = x-k*pi/2 25 * in [-pi/4 , +pi/4], and let n = k mod 4. 26 * We have 27 * 28 * n ieee_sin(x) ieee_cos(x) ieee_tan(x) 29 * ---------------------------------------------------------- 30 * 0 S C T 31 * 1 C -S -1/T 32 * 2 -S -C T 33 * 3 -C S -1/T 34 * ---------------------------------------------------------- 35 * 36 * Special cases: 37 * Let trig be any of sin, cos, or tan. 38 * trig(+-INF) is NaN, with signals; 39 * trig(NaN) is that NaN; 40 * 41 * Accuracy: 42 * TRIG(x) returns trig(x) nearly rounded 43 */ 44 45 #include "fdlibm.h" 46 47 #ifdef __STDC__ 48 double ieee_cos(double x) 49 #else 50 double ieee_cos(x) 51 double x; 52 #endif 53 { 54 double y[2],z=0.0; 55 int n, ix; 56 57 /* High word of x. */ 58 ix = __HI(x); 59 60 /* |x| ~< pi/4 */ 61 ix &= 0x7fffffff; 62 if(ix <= 0x3fe921fb) return __kernel_cos(x,z); 63 64 /* ieee_cos(Inf or NaN) is NaN */ 65 else if (ix>=0x7ff00000) return x-x; 66 67 /* argument reduction needed */ 68 else { 69 n = __ieee754_rem_pio2(x,y); 70 switch(n&3) { 71 case 0: return __kernel_cos(y[0],y[1]); 72 case 1: return -__kernel_sin(y[0],y[1],1); 73 case 2: return -__kernel_cos(y[0],y[1]); 74 default: 75 return __kernel_sin(y[0],y[1],1); 76 } 77 } 78 } 79
