1 /* @(#)s_tan.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_tan.c,v 1.8 1997/10/09 11:33:35 lukem Exp $"); 16 #endif 17 18 /* tan(x) 19 * Return tangent function of x. 20 * 21 * kernel function: 22 * __kernel_tan ... tangent 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 #ifdef __STDC__ 52 double tan(double x) 53 #else 54 double tan(x) 55 double x; 56 #endif 57 { 58 double y[2],z=0.0; 59 int32_t n, ix; 60 61 /* High word of x. */ 62 GET_HIGH_WORD(ix,x); 63 64 /* |x| ~< pi/4 */ 65 ix &= 0x7fffffff; 66 if(ix <= 0x3fe921fb) return __kernel_tan(x,z,1); 67 68 /* tan(Inf or NaN) is NaN */ 69 else if (ix>=0x7ff00000) return x-x; /* NaN */ 70 71 /* argument reduction needed */ 72 else { 73 n = __ieee754_rem_pio2(x,y); 74 return __kernel_tan(y[0],y[1],1-((n&1)<<1)); /* 1 -- n even 75 -1 -- n odd */ 76 } 77 } 78