usr/src/lib/libm/common/LD/log1pl.c

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