workbench/libs/mathtrans/spexp.c

   1 /*
   2     Copyright © 1995-2003, The AROS Development Team. All rights reserved.
   3     $Id$
   4 */
   5
   6 #include "mathtrans_intern.h"
   7
   8 /*
   9     FUNCTION
  10       Calculate e^x
  11
  12     RESULT
  13       Motorola fast floating point number
  14
  15       flags:
  16         zero     : result is zero
  17         negative : 0
  18         overflow : the result was out of range for the ffp-format
  19
  20     NOTES
  21
  22     EXAMPLE
  23
  24     BUGS
  25
  26     SEE ALSO
  27
  28     INTERNALS
  29      <code>
  30       e^(>= 44): return FFP_Pinfty;
  31      </code>
  32
  33     HISTORY
  34 */
  35
  36 AROS_LH1(float, SPExp,
  37     AROS_LHA(float, fnum1, D0),
  38     struct Library *, MathTransBase, 13, MathTrans
  39 )
  40 {
  41     AROS_LIBFUNC_INIT
  42
  43     const LONG ExpTable[] =
  44     {
  45         0x8fa1fe6f,  /* e^32  */
  46         0x87975e58,  /* e^16  */
  47         0xba4f534c,  /* e^8   */
  48         0xda648146,  /* e^4   */
  49         0xec732543,  /* e^2   */
  50         0xadf85442,  /* e^1   */
  51         0xD3094C41,  /* e^(1/2) */
  52         0xA45aF241,  /* e^(1/4) */
  53         0x910b0241,  /* e^(1/8) */
  54         0x88415b41,  /* e^(1/16) */
  55         0x84102b41,  /* e^(1/32) */
  56         0x82040541,  /* e^(1/64) */
  57         0x81010141,  /* e^(1/128) */
  58         0x80804041,  /* e^(1/256) */
  59         0x80401041,  /* e^(1/512) */
  60         0x80200441,  /* e^(1/1024) */
  61         0x80100141,  /* e^(1/2048) */
  62         0x80080041,  /* e^(1/4096) */
  63         0x80040041,  /* e^(1/8192) */
  64         0x80020041,  /* e^(1/16384) */
  65         0x80010041,  /* e^(1/32768) */
  66         0x80008041,  /* e^(1/65536) */
  67         0x80004041,  /* e^(1/131072) */
  68         0x80002041,  /* e^(1/262144) */
  69         0x80001041,  /* e^(1/524288) */
  70         0x80000841,  /* e^(1/1048576) */
  71         0x80000441,  /* e^(1/2097152) */
  72         0x80000241,  /* e^(1/4194304) */
  73         0x80000141   /* e^(1/8388608) */
  74     };
  75
  76     ULONG Res, i;
  77     LONG Mantisse;
  78     char Exponent;
  79
  80     Exponent = (fnum1 & FFPExponent_Mask) - 0x41;
  81
  82     /* e^0 = 1, e^(2^(<=-24)) = 1 */
  83     if ( 0 == fnum1 || Exponent <= -24 ) return one;
  84
  85     /* e^(>= 44) = overflow = infinity) */
  86     if (Exponent > 5)
  87     {
  88         SetSR(Overflow_Bit, Zero_Bit | Negative_Bit | Overflow_Bit);
  89         return FFP_Pinfty;
  90     }
  91
  92     i = 5 - Exponent;
  93
  94     Mantisse = (fnum1 & FFPMantisse_Mask);
  95     Res = ExpTable[i++];
  96     Mantisse <<= 1;
  97
  98     while ( 0 != Mantisse && i <= 28 )
  99     {
 100         /* is the highest bit set? */
 101         if ( Mantisse < 0 )
 102         {
 103             Res = SPMul(Res, ExpTable[i]);
 104             if (0 == Res)
 105             {
 106                 SetSR(Zero_Bit, Zero_Bit | Negative_Bit | Overflow_Bit);
 107                 return Res;
 108             }
 109             if (FFP_Pinfty == Res)
 110             {
 111                 SetSR(Overflow_Bit, Zero_Bit | Negative_Bit | Overflow_Bit);
 112                 return Res;
 113             }
 114         }
 115         i++;
 116         Mantisse <<= 1;
 117     }
 118
 119     if ( (char) fnum1 < 0) return SPDiv(one, Res);
 120
 121     return Res;
 122
 123     AROS_LIBFUNC_EXIT
 124 }