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 /* cos(x) 14 * Return cosine function of x. 15 * 16 * kernel function: 17 * __kernel_sin ... sine function on [-pi/4,pi/4] 18 * __kernel_cos ... cosine function on [-pi/4,pi/4] 19 * __ieee754_rem_pio2 ... argument reduction routine 20 * 21 * Method. 22 * Let S,C and T denote the sin, cos and tan respectively on 23 * [-PI/4, +PI/4]. Reduce the argument x to y1+y2 = x-k*pi/2 24 * in [-pi/4 , +pi/4], and let n = k mod 4. 25 * We have 26 * 27 * n sin(x) cos(x) tan(x) 28 * ---------------------------------------------------------- 29 * 0 S C T 30 * 1 C -S -1/T 31 * 2 -S -C T 32 * 3 -C S -1/T 33 * ---------------------------------------------------------- 34 * 35 * Special cases: 36 * Let trig be any of sin, cos, or tan. 37 * trig(+-INF) is NaN, with signals; 38 * trig(NaN) is that NaN; 39 * 40 * Accuracy: 41 * TRIG(x) returns trig(x) nearly rounded 42 */ 43 44 /* LINTLIBRARY */ 45 46 #include <sys/cdefs.h> 47 #include <float.h> 48 #include <math.h> 49 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 81 #if LDBL_MANT_DIG == 53 82 #ifdef lint 83 /* PROTOLIB1 */ 84 long double cosl(long double); 85 #else /* lint */ 86 __weak_alias(cosl, cos); 87 #endif /* lint */ 88 #endif /* LDBL_MANT_DIG == 53 */ 89