usr/src/lib/libm/common/C/exp10.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  * Copyright 2011 Nexenta Systems, Inc.  All rights reserved.
  23  */
  24 /*
  25  * Copyright 2006 Sun Microsystems, Inc.  All rights reserved.
  26  * Use is subject to license terms.
  27  */
  28
  29 /* INDENT OFF */
  30 /*
  31  * exp10(x)
  32  * Code by K.C. Ng for SUN 4.0 libm.
  33  * Method :
  34  *      n = nint(x*(log10/log2));
  35  *      exp10(x) = 10**x = exp(x*ln(10)) = exp(n*ln2+(x*ln10-n*ln2))
  36  *               = 2**n*exp(ln10*(x-n*log2/log10)))
  37  *      If x is an integer < 23 then use repeat multiplication. For
  38  *      10**22 is the largest representable integer.
  39  */
  40 /* INDENT ON */
  41
  42 #include "libm.h"
  43
  44 static const double C[] = {
  45         3.3219280948736234787,  /* log(10)/log(2) */
  46         2.3025850929940456840,  /* log(10) */
  47         3.0102999565860955045E-1,       /* log(2)/log(10) high */
  48         5.3716447674669983622E-12,      /* log(2)/log(10) low */
  49         0.0,
  50         0.5,
  51         1.0,
  52         10.0,
  53         1.0e300,
  54         1.0e-300,
  55 };
  56
  57 #define lg10    C[0]
  58 #define ln10    C[1]
  59 #define logt2hi C[2]
  60 #define logt2lo C[3]
  61 #define zero    C[4]
  62 #define half    C[5]
  63 #define one     C[6]
  64 #define ten     C[7]
  65 #define huge    C[8]
  66 #define tiny    C[9]
  67
  68 double
  69 exp10(double x) {
  70         double  t, pt;
  71         int     ix, hx, k;
  72
  73         ix = ((int *)&x)[HIWORD];
  74         hx = ix & ~0x80000000;
  75
  76         if (hx >= 0x4074a000) { /* |x| >= 330 or x is nan */
  77                 if (hx >= 0x7ff00000) { /* x is inf or nan */
  78                         if (ix == 0xfff00000 && ((int *)&x)[LOWORD] == 0)
  79                                 return (zero);
  80                         return (x * x);
  81                 }
  82                 t = (ix < 0)? tiny : huge;
  83                 return (t * t);
  84         }
  85
  86         if (hx < 0x3c000000)
  87                 return (one + x);
  88
  89         k = (int)x;
  90         if (0 <= k && k < 23 && (double)k == x) {
  91                 /* x is a small positive integer */
  92                 t = one;
  93                 pt = ten;
  94                 if (k & 1)
  95                         t = ten;
  96                 k >>= 1;
  97                 while (k) {
  98                         pt *= pt;
  99                         if (k & 1)
 100                                 t *= pt;
 101                         k >>= 1;
 102                 }
 103                 return (t);
 104         }
 105         t = x * lg10;
 106         k = (int)((ix < 0)? t - half : t + half);
 107         return (scalbn(exp(ln10 * ((x - k * logt2hi) - k * logt2lo)), k));
 108 }