1 /* $NetBSD: n_tan.c,v 1.4 2002/06/15 00:10:18 matt 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. All advertising materials mentioning features or use of this software 15 * must display the following acknowledgement: 16 * This product includes software developed by the University of 17 * California, Berkeley and its contributors. 18 * 4. Neither the name of the University nor the names of its contributors 19 * may be used to endorse or promote products derived from this software 20 * without specific prior written permission. 21 * 22 * THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND 23 * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE 24 * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE 25 * ARE DISCLAIMED. IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE 26 * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL 27 * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS 28 * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) 29 * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT 30 * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY 31 * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF 32 * SUCH DAMAGE. 33 */ 34 35 #ifndef lint 36 #if 0 37 static char sccsid[] = "@(#)tan.c 8.1 (Berkeley) 6/4/93"; 38 #endif 39 #endif /* not lint */ 40 41 #include "mathimpl.h" 42 #include "trig.h" 43 double 44 tan(double x) 45 { 46 double a,z,ss,cc,c; 47 int k; 48 49 if(!finite(x)) /* tan(NaN) and tan(INF) must be NaN */ 50 return x-x; 51 x = drem(x,PI); /* reduce x into [-PI/2, PI/2] */ 52 a = copysign(x,__one); /* ... = abs(x) */ 53 if (a >= PIo4) { 54 k = 1; 55 x = copysign(PIo2-a,x); 56 } 57 else { 58 k = 0; 59 if (a < __small) { 60 z=__big+a; 61 return x; 62 } 63 } 64 z = x*x; 65 cc = cos__C(z); 66 ss = sin__S(z); 67 z *= __half; /* Next get c = cos(x) accurately */ 68 c = (z >= thresh ? __half-((z-__half)-cc) : __one-(z-cc)); 69 if (k == 0) 70 return x+(x*(z-(cc-ss)))/c; /* ... sin/cos */ 71 #ifdef national 72 else if (x == __zero) 73 return copysign(fmax,x); /* no inf on 32k */ 74 #endif /* national */ 75 else 76 return c/(x+x*ss); /* ... cos/sin */ 77 } 78