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 #if defined(ELFOBJ)
  31 #pragma weak log1pl = __log1pl
  32 #endif
  33 
  34 /*
  35  * log1pl(x)
  36  * Kahan's trick based on log(1+x)/x being a slow varying function.
  37  */
  38 
  39 #include "libm.h"
  40 
  41 #if defined(__x86)
  42 #define __swapRD        __swap87RD
  43 #endif
  44 extern enum fp_direction_type __swapRD(enum fp_direction_type);
  45 
  46 long double
  47 log1pl(long double x) {
  48         long double y;
  49         enum fp_direction_type rd;
  50 
  51         if (x != x)
  52                 return (x + x);
  53         if (x < -1.L)
  54                 return (logl(x));
  55         rd = __swapRD(fp_nearest);
  56         y = 1.L + x;
  57         if (y != 1.L)
  58                 if (y == x)
  59                         x = logl(x);
  60                 else
  61                         x *= logl(y) / (y - 1.L);
  62         if (rd != fp_nearest)
  63                 (void) __swapRD(rd);
  64         return (x);
  65 }