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 14 static char rcsid[] = "$FreeBSD$"; 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 <float.h> 49 50 #include "math.h" 51 #include "math_private.h" 52 53 double 54 cos(double x) 55 { 56 double y[2],z=0.0; 57 int32_t n, ix; 58 59 /* High word of x. */ 60 GET_HIGH_WORD(ix,x); 61 62 /* |x| ~< pi/4 */ 63 ix &= 0x7fffffff; 64 if(ix <= 0x3fe921fb) { 65 if(ix<0x3e400000) /* if x < 2**-27 */ 66 if(((int)x)==0) return 1.0; /* generate inexact */ 67 return __kernel_cos(x,z); 68 } 69 70 /* cos(Inf or NaN) is NaN */ 71 else if (ix>=0x7ff00000) return x-x; 72 73 /* argument reduction needed */ 74 else { 75 n = __ieee754_rem_pio2(x,y); 76 switch(n&3) { 77 case 0: return __kernel_cos(y[0],y[1]); 78 case 1: return -__kernel_sin(y[0],y[1],1); 79 case 2: return -__kernel_cos(y[0],y[1]); 80 default: 81 return __kernel_sin(y[0],y[1],1); 82 } 83 } 84 } 85 86 #if (LDBL_MANT_DIG == 53) 87 __weak_reference(cos, cosl); 88 #endif 89