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 log10l = __log10l
  32 #endif
  33 
  34 /*
  35  * log10l(X)
  36  *
  37  * Method :
  38  *      Let log10_2hi = leading 98(SPARC)/49(x86) bits of log10(2) and
  39  *          log10_2lo = log10(2) - log10_2hi,
  40  *          ivln10   = 1/log(10) rounded.
  41  *      Then
  42  *              n = ilogb(x),
  43  *              if (n<0)  n = n+1;
  44  *              x = scalbn(x,-n);
  45  *              LOG10(x) := n*log10_2hi + (n*log10_2lo + ivln10*log(x))
  46  *
  47  * Note1:
  48  *      For fear of destroying log10(10**n)=n, the rounding mode is
  49  *      set to Round-to-Nearest.
  50  *
  51  * Special cases:
  52  *      log10(x) is NaN with signal if x < 0;
  53  *      log10(+INF) is +INF with no signal; log10(0) is -INF with signal;
  54  *      log10(NaN) is that NaN with no signal;
  55  *      log10(10**N) = N  for N=0,1,...,22.
  56  *
  57  * Constants:
  58  * The hexadecimal values are the intended ones for the following constants.
  59  * The decimal values may be used, provided that the compiler will convert
  60  * from decimal to binary accurately enough to produce the hexadecimal values
  61  * shown.
  62  */
  63 
  64 #include "libm.h"
  65 #include "longdouble.h"
  66 
  67 #if defined(__x86)
  68 #define __swapRD        __swap87RD
  69 #endif
  70 extern enum fp_direction_type __swapRD(enum fp_direction_type);
  71 
  72 static const long double
  73         zero      = 0.0L,
  74         ivln10    = 4.342944819032518276511289189166050822944e-0001L,
  75         one       = 1.0L,
  76 #if defined(__x86)
  77         log10_2hi = 3.010299956639803653501985536422580480576e-01L,
  78         log10_2lo = 8.298635403410822349787106337291183585413e-16L;
  79 #elif defined(__sparc)
  80         log10_2hi = 3.010299956639811952137388947242098603469e-01L,
  81         log10_2lo = 2.831664213089468167896664371953210945664e-31L;
  82 #else
  83 #error Unknown Architecture!
  84 #endif
  85 
  86 long double
  87 log10l(long double x) {
  88         long double y, z;
  89         enum fp_direction_type rd;
  90         int n;
  91 
  92         if (!finitel(x))
  93                 return (x + fabsl(x));  /* x is +-INF or NaN */
  94         else if (x > zero) {
  95                 n = ilogbl(x);
  96                 if (n < 0)
  97                         n += 1;
  98                 rd = __swapRD(fp_nearest);
  99                 y = n;
 100                 x = scalbnl(x, -n);
 101                 z = y * log10_2lo + ivln10 * logl(x);
 102                 z += y * log10_2hi;
 103                 if (rd != fp_nearest)
 104                         (void) __swapRD(rd);
 105                 return (z);
 106         } else if (x == zero)   /* -INF */
 107                 return (-one / zero);
 108         else                    /* x <0, return NaN */
 109                 return (zero / zero);
 110 }