1 /* @(#)s_sin.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[] = "$Id: s_sin.c,v 1.3 1994/02/18 02:26:59 jtc Exp $"; 15 #endif 16 17 /* sin(x) 18 * Return sine function of x. 19 * 20 * kernel function: 21 * __kernel_sin ... sine function on [-pi/4,pi/4] 22 * __kernel_cos ... cose 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 50 #ifdef __STDC__ 51 static const double one=1.0; 52 #else 53 static double one=1.0; 54 #endif 55 56 #ifdef __STDC__ 57 double sin(double x) 58 #else 59 double sin(x) 60 double x; 61 #endif 62 { 63 double y[2],z=0.0; 64 int n, ix; 65 66 /* High word of x. */ 67 ix = *( (((*(int*)&one)>>29)^1) + (int*)&x); 68 69 /* |x| ~< pi/4 */ 70 ix &= 0x7fffffff; 71 if(ix <= 0x3fe921fb) return __kernel_sin(x,z,0); 72 73 /* sin(Inf or NaN) is NaN */ 74 else if (ix>=0x7ff00000) return x-x; 75 76 /* argument reduction needed */ 77 else { 78 n = __ieee754_rem_pio2(x,y); 79 switch(n&3) { 80 case 0: return __kernel_sin(y[0],y[1],1); 81 case 1: return __kernel_cos(y[0],y[1]); 82 case 2: return -__kernel_sin(y[0],y[1],1); 83 default: 84 return -__kernel_cos(y[0],y[1]); 85 } 86 } 87 } 88