1 /* @(#)s_cos.c 5.1 93/09/24 */ 2 /* 3 * ==================================================== 4 * Copyright (C) 1993 by Sun Microsystems, Inc. All rights reserved. 5 * 6 * Developed at SunPro, a Sun Microsystems, Inc. business. 7 * Permission to use, copy, modify, and distribute this 8 * software is freely granted, provided that this notice 9 * is preserved. 10 * ==================================================== 11 */ 12 13 #include <sys/cdefs.h> 14 #if defined(LIBM_SCCS) && !defined(lint) 15 __RCSID("$NetBSD: s_cos.c,v 1.10 2002/05/26 22:01:54 wiz Exp $"); 16 #endif 17 18 /* cos(x) 19 * Return cosine function of x. 20 * 21 * kernel function: 22 * __kernel_sin ... sine function on [-pi/4,pi/4] 23 * __kernel_cos ... cosine function on [-pi/4,pi/4] 24 * __ieee754_rem_pio2 ... argument reduction routine 25 * 26 * Method. 27 * Let S,C and T denote the sin, cos and tan respectively on 28 * [-PI/4, +PI/4]. Reduce the argument x to y1+y2 = x-k*pi/2 29 * in [-pi/4 , +pi/4], and let n = k mod 4. 30 * We have 31 * 32 * n sin(x) cos(x) tan(x) 33 * ---------------------------------------------------------- 34 * 0 S C T 35 * 1 C -S -1/T 36 * 2 -S -C T 37 * 3 -C S -1/T 38 * ---------------------------------------------------------- 39 * 40 * Special cases: 41 * Let trig be any of sin, cos, or tan. 42 * trig(+-INF) is NaN, with signals; 43 * trig(NaN) is that NaN; 44 * 45 * Accuracy: 46 * TRIG(x) returns trig(x) nearly rounded 47 */ 48 49 #include "math.h" 50 #include "math_private.h" 51 52 double 53 cos(double x) 54 { 55 double y[2],z=0.0; 56 int32_t n, ix; 57 58 /* High word of x. */ 59 GET_HIGH_WORD(ix,x); 60 61 /* |x| ~< pi/4 */ 62 ix &= 0x7fffffff; 63 if(ix <= 0x3fe921fb) return __kernel_cos(x,z); 64 65 /* cos(Inf or NaN) is NaN */ 66 else if (ix>=0x7ff00000) return x-x; 67 68 /* argument reduction needed */ 69 else { 70 n = __ieee754_rem_pio2(x,y); 71 switch(n&3) { 72 case 0: return __kernel_cos(y[0],y[1]); 73 case 1: return -__kernel_sin(y[0],y[1],1); 74 case 2: return -__kernel_cos(y[0],y[1]); 75 default: 76 return __kernel_sin(y[0],y[1],1); 77 } 78 } 79 } 80