1 /* $NetBSD: n_atanhf.c,v 1.1 2016/09/21 14:11:40 christos Exp $ */ 2 /* 3 * Copyright (c) 1985, 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 #include <sys/cdefs.h> 31 __RCSID("$NetBSD: n_atanhf.c,v 1.1 2016/09/21 14:11:40 christos Exp $"); 32 33 #ifndef lint 34 #if 0 35 static char sccsid[] = "@(#)atanh.c 8.1 (Berkeley) 6/4/93"; 36 #endif 37 #endif /* not lint */ 38 39 /* ATANH(X) 40 * RETURN THE HYPERBOLIC ARC TANGENT OF X 41 * DOUBLE PRECISION (VAX D format 56 bits, IEEE DOUBLE 53 BITS) 42 * CODED IN C BY K.C. NG, 1/8/85; 43 * REVISED BY K.C. NG on 2/7/85, 3/7/85, 8/18/85. 44 * 45 * Required kernel function: 46 * log1p(x) ...return log(1+x) 47 * 48 * Method : 49 * Return 50 * 1 2x x 51 * atanh(x) = --- * log(1 + -------) = 0.5 * log1p(2 * --------) 52 * 2 1 - x 1 - x 53 * 54 * Special cases: 55 * atanh(x) is NaN if |x| > 1 with signal; 56 * atanh(NaN) is that NaN with no signal; 57 * atanh(+-1) is +-INF with signal. 58 * 59 * Accuracy: 60 * atanh(x) returns the exact hyperbolic arc tangent of x nearly rounded. 61 * In a test run with 512,000 random arguments on a VAX, the maximum 62 * observed error was 1.87 ulps (units in the last place) at 63 * x= -3.8962076028810414000e-03. 64 */ 65 #include "mathimpl.h" 66 67 #if defined(__vax__)||defined(tahoe) 68 #include <errno.h> 69 #endif /* defined(__vax__)||defined(tahoe) */ 70 71 float 72 atanhf(float x) 73 { 74 float z; 75 z = copysignf(0.5,x); 76 x = copysignf(x,1.0); 77 #if defined(__vax__)||defined(tahoe) 78 if (x == 1.0) { 79 return(copysignf(1.0,z)*infnan(ERANGE)); /* sign(x)*INF */ 80 } 81 #endif /* defined(__vax__)||defined(tahoe) */ 82 x = x/(1.0-x); 83 return( z*log1pf(x+x) ); 84 } 85