1 /* 2 * Copyright (c) 1998, 2001, Oracle and/or its affiliates. All rights reserved. 3 * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER. 4 * 5 * This code is free software; you can redistribute it and/or modify it 6 * under the terms of the GNU General Public License version 2 only, as 7 * published by the Free Software Foundation. Oracle designates this 8 * particular file as subject to the "Classpath" exception as provided 9 * by Oracle in the LICENSE file that accompanied this code. 10 * 11 * This code is distributed in the hope that it will be useful, but WITHOUT 12 * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or 13 * FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License 14 * version 2 for more details (a copy is included in the LICENSE file that 15 * accompanied this code). 16 * 17 * You should have received a copy of the GNU General Public License version 18 * 2 along with this work; if not, write to the Free Software Foundation, 19 * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA. 20 * 21 * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA 22 * or visit www.oracle.com if you need additional information or have any 23 * questions. 24 */ 25 26 /* tan(x) 27 * Return tangent function of x. 28 * 29 * kernel function: 30 * __kernel_tan ... tangent function on [-pi/4,pi/4] 31 * __ieee754_rem_pio2 ... argument reduction routine 32 * 33 * Method. 34 * Let S,C and T denote the sin, cos and tan respectively on 35 * [-PI/4, +PI/4]. Reduce the argument x to y1+y2 = x-k*pi/2 36 * in [-pi/4 , +pi/4], and let n = k mod 4. 37 * We have 38 * 39 * n sin(x) cos(x) tan(x) 40 * ---------------------------------------------------------- 41 * 0 S C T 42 * 1 C -S -1/T 43 * 2 -S -C T 44 * 3 -C S -1/T 45 * ---------------------------------------------------------- 46 * 47 * Special cases: 48 * Let trig be any of sin, cos, or tan. 49 * trig(+-INF) is NaN, with signals; 50 * trig(NaN) is that NaN; 51 * 52 * Accuracy: 53 * TRIG(x) returns trig(x) nearly rounded 54 */ 55 56 #include "fdlibm.h" 57 58 #ifdef __STDC__ tan(double x)59 double tan(double x) 60 #else 61 double tan(x) 62 double x; 63 #endif 64 { 65 double y[2],z=0.0; 66 int n, ix; 67 68 /* High word of x. */ 69 ix = __HI(x); 70 71 /* |x| ~< pi/4 */ 72 ix &= 0x7fffffff; 73 if(ix <= 0x3fe921fb) return __kernel_tan(x,z,1); 74 75 /* tan(Inf or NaN) is NaN */ 76 else if (ix>=0x7ff00000) return x-x; /* NaN */ 77 78 /* argument reduction needed */ 79 else { 80 n = __ieee754_rem_pio2(x,y); 81 return __kernel_tan(y[0],y[1],1-((n&1)<<1)); /* 1 -- n even 82 -1 -- n odd */ 83 } 84 } 85