1 /* 2 * CDDL HEADER START 3 * 4 * The contents of this file are subject to the terms of the 5 * Common Development and Distribution License (the "License"). 6 * You may not use this file except in compliance with the License. 7 * 8 * You can obtain a copy of the license at usr/src/OPENSOLARIS.LICENSE 9 * or http://www.opensolaris.org/os/licensing. 10 * See the License for the specific language governing permissions 11 * and limitations under the License. 12 * 13 * When distributing Covered Code, include this CDDL HEADER in each 14 * file and include the License file at usr/src/OPENSOLARIS.LICENSE. 15 * If applicable, add the following below this CDDL HEADER, with the 16 * fields enclosed by brackets "[]" replaced with your own identifying 17 * information: Portions Copyright [yyyy] [name of copyright owner] 18 * 19 * CDDL HEADER END 20 */ 21 22 /* 23 * Copyright 2011 Nexenta Systems, Inc. All rights reserved. 24 */ 25 /* 26 * Copyright 2006 Sun Microsystems, Inc. All rights reserved. 27 * Use is subject to license terms. 28 */ 29 30 #pragma weak atanh = __atanh 31 32 /* INDENT OFF */ 33 /* 34 * atanh(x) 35 * Code originated from 4.3bsd. 36 * Modified by K.C. Ng for SUN 4.0 libm. 37 * Method : 38 * 1 2x x 39 * atanh(x) = --- * log(1 + -------) = 0.5 * log1p(2 * --------) 40 * 2 1 - x 1 - x 41 * Note: to guarantee atanh(-x) = -atanh(x), we use 42 * sign(x) |x| 43 * atanh(x) = ------- * log1p(2*-------). 44 * 2 1 - |x| 45 * 46 * Special cases: 47 * atanh(x) is NaN if |x| > 1 with signal; 48 * atanh(NaN) is that NaN with no signal; 49 * atanh(+-1) is +-INF with signal. 50 */ 51 /* INDENT ON */ 52 53 #include "libm.h" 54 #include "libm_synonyms.h" 55 #include "libm_protos.h" 56 #include <math.h> 57 58 double 59 atanh(double x) { 60 double t; 61 62 if (isnan(x)) 63 return (x * x); /* switched from x + x for Cheetah */ 64 t = fabs(x); 65 if (t > 1.0) 66 return (_SVID_libm_err(x, x, 30)); /* sNaN */ 67 if (t == 1.0) 68 return (_SVID_libm_err(x, x, 31)); /* x/0; */ 69 t = t / (1.0 - t); 70 return (copysign(0.5, x) * log1p(t + t)); 71 } 72