1 /* $NetBSD: n_tan.c,v 1.5 2003/08/07 16:44:52 agc Exp $ */ 2 /* 3 * Copyright (c) 1987, 1993 4 * The Regents of the University of California. All rights reserved. 5 * 6 * Redistribution and use in source and binary forms, with or without 7 * modification, are permitted provided that the following conditions 8 * are met: 9 * 1. Redistributions of source code must retain the above copyright 10 * notice, this list of conditions and the following disclaimer. 11 * 2. Redistributions in binary form must reproduce the above copyright 12 * notice, this list of conditions and the following disclaimer in the 13 * documentation and/or other materials provided with the distribution. 14 * 3. Neither the name of the University nor the names of its contributors 15 * may be used to endorse or promote products derived from this software 16 * without specific prior written permission. 17 * 18 * THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND 19 * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE 20 * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE 21 * ARE DISCLAIMED. IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE 22 * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL 23 * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS 24 * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) 25 * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT 26 * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY 27 * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF 28 * SUCH DAMAGE. 29 */ 30 31 #ifndef lint 32 #if 0 33 static char sccsid[] = "@(#)tan.c 8.1 (Berkeley) 6/4/93"; 34 #endif 35 #endif /* not lint */ 36 37 #include "mathimpl.h" 38 #include "trig.h" 39 double 40 tan(double x) 41 { 42 double a,z,ss,cc,c; 43 int k; 44 45 if(!finite(x)) /* tan(NaN) and tan(INF) must be NaN */ 46 return x-x; 47 x = drem(x,PI); /* reduce x into [-PI/2, PI/2] */ 48 a = copysign(x,__one); /* ... = abs(x) */ 49 if (a >= PIo4) { 50 k = 1; 51 x = copysign(PIo2-a,x); 52 } 53 else { 54 k = 0; 55 if (a < __small) { 56 z=__big+a; 57 return x; 58 } 59 } 60 z = x*x; 61 cc = cos__C(z); 62 ss = sin__S(z); 63 z *= __half; /* Next get c = cos(x) accurately */ 64 c = (z >= thresh ? __half-((z-__half)-cc) : __one-(z-cc)); 65 if (k == 0) 66 return x+(x*(z-(cc-ss)))/c; /* ... sin/cos */ 67 #ifdef national 68 else if (x == __zero) 69 return copysign(fmax,x); /* no inf on 32k */ 70 #endif /* national */ 71 else 72 return c/(x+x*ss); /* ... cos/sin */ 73 } 74