s_cos.c revision 97409
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#ifndef lint 14static char rcsid[] = "$FreeBSD: head/lib/msun/src/s_cos.c 97409 2002-05-28 17:51:46Z alfred $"; 15#endif 16 17/* cos(x) 18 * Return cosine function of x. 19 * 20 * kernel function: 21 * __kernel_sin ... sine function on [-pi/4,pi/4] 22 * __kernel_cos ... cosine function on [-pi/4,pi/4] 23 * __ieee754_rem_pio2 ... argument reduction routine 24 * 25 * Method. 26 * Let S,C and T denote the sin, cos and tan respectively on 27 * [-PI/4, +PI/4]. Reduce the argument x to y1+y2 = x-k*pi/2 28 * in [-pi/4 , +pi/4], and let n = k mod 4. 29 * We have 30 * 31 * n sin(x) cos(x) tan(x) 32 * ---------------------------------------------------------- 33 * 0 S C T 34 * 1 C -S -1/T 35 * 2 -S -C T 36 * 3 -C S -1/T 37 * ---------------------------------------------------------- 38 * 39 * Special cases: 40 * Let trig be any of sin, cos, or tan. 41 * trig(+-INF) is NaN, with signals; 42 * trig(NaN) is that NaN; 43 * 44 * Accuracy: 45 * TRIG(x) returns trig(x) nearly rounded 46 */ 47 48#include "math.h" 49#include "math_private.h" 50 51 double __generic_cos(double x) 52{ 53 double y[2],z=0.0; 54 int32_t n, ix; 55 56 /* High word of x. */ 57 GET_HIGH_WORD(ix,x); 58 59 /* |x| ~< pi/4 */ 60 ix &= 0x7fffffff; 61 if(ix <= 0x3fe921fb) return __kernel_cos(x,z); 62 63 /* cos(Inf or NaN) is NaN */ 64 else if (ix>=0x7ff00000) return x-x; 65 66 /* argument reduction needed */ 67 else { 68 n = __ieee754_rem_pio2(x,y); 69 switch(n&3) { 70 case 0: return __kernel_cos(y[0],y[1]); 71 case 1: return -__kernel_sin(y[0],y[1],1); 72 case 2: return -__kernel_cos(y[0],y[1]); 73 default: 74 return __kernel_sin(y[0],y[1],1); 75 } 76 } 77} 78