usr/src/lib/libast/common/uwin/atanh.c

   1 #include "FEATURE/uwin"
   2
   3 #if !_UWIN || _lib_atanh
   4
   5 void _STUB_atanh(){}
   6
   7 #else
   8
   9 /*
  10  * Copyright (c) 1985, 1993
  11  *      The Regents of the University of California.  All rights reserved.
  12  *
  13  * Redistribution and use in source and binary forms, with or without
  14  * modification, are permitted provided that the following conditions
  15  * are met:
  16  * 1. Redistributions of source code must retain the above copyright
  17  *    notice, this list of conditions and the following disclaimer.
  18  * 2. Redistributions in binary form must reproduce the above copyright
  19  *    notice, this list of conditions and the following disclaimer in the
  20  *    documentation and/or other materials provided with the distribution.
  21  * 3. Neither the name of the University nor the names of its contributors
  22  *    may be used to endorse or promote products derived from this software
  23  *    without specific prior written permission.
  24  *
  25  * THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND
  26  * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
  27  * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
  28  * ARE DISCLAIMED.  IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE
  29  * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
  30  * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
  31  * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
  32  * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
  33  * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
  34  * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
  35  * SUCH DAMAGE.
  36  */
  37
  38 static char sccsid[] = "@(#)atanh.c     8.1 (Berkeley) 6/4/93";
  39
  40 /* ATANH(X)
  41  * RETURN THE HYPERBOLIC ARC TANGENT OF X
  42  * DOUBLE PRECISION (VAX D format 56 bits, IEEE DOUBLE 53 BITS)
  43  * CODED IN C BY K.C. NG, 1/8/85;
  44  * REVISED BY K.C. NG on 2/7/85, 3/7/85, 8/18/85.
  45  *
  46  * Required kernel function:
  47  *      log1p(x)        ...return log(1+x)
  48  *
  49  * Method :
  50  *      Return
  51  *                          1              2x                          x
  52  *              atanh(x) = --- * log(1 + -------) = 0.5 * log1p(2 * --------)
  53  *                          2             1 - x                      1 - x
  54  *
  55  * Special cases:
  56  *      atanh(x) is NaN if |x| > 1 with signal;
  57  *      atanh(NaN) is that NaN with no signal;
  58  *      atanh(+-1) is +-INF with signal.
  59  *
  60  * Accuracy:
  61  *      atanh(x) returns the exact hyperbolic arc tangent of x nearly rounded.
  62  *      In a test run with 512,000 random arguments on a VAX, the maximum
  63  *      observed error was 1.87 ulps (units in the last place) at
  64  *      x= -3.8962076028810414000e-03.
  65  */
  66 #include "mathimpl.h"
  67
  68 #if defined(vax)||defined(tahoe)
  69 #include <errno.h>
  70 #endif  /* defined(vax)||defined(tahoe) */
  71
  72 extern double atanh(x)
  73 double x;
  74 {
  75         double z;
  76         z = copysign(0.5,x);
  77         x = copysign(x,1.0);
  78 #if defined(vax)||defined(tahoe)
  79         if (x == 1.0) {
  80             return(copysign(1.0,z)*infnan(ERANGE));     /* sign(x)*INF */
  81         }
  82 #endif  /* defined(vax)||defined(tahoe) */
  83         x = x/(1.0-x);
  84         return( z*log1p(x+x) );
  85 }
  86
  87 #endif