workbench/libs/mathffp/spflt.c

   1 /*
   2     Copyright © 1995-2004, The AROS Development Team. All rights reserved.
   3     $Id$
   4 */
   5
   6 #include "mathffp_intern.h"
   7
   8 /*****************************************************************************
   9
  10     NAME */
  11
  12         AROS_LH1(float, SPFlt,
  13
  14 /*  SYNOPSIS */
  15         AROS_LHA(LONG, inum, D0),
  16
  17 /*  LOCATION */
  18         struct LibHeader *, MathBase, 6, Mathffp)
  19
  20 /*  FUNCTION
  21
  22     INPUTS
  23
  24     RESULT
  25         FFP number
  26
  27         Flags:
  28           zero     : result is zero
  29           negative : result is negative
  30           overflow : ffp is not exactly the integer
  31
  32     BUGS
  33
  34     INTERNALS
  35         Return zero for x == 0.
  36         If x < 0 set the sign-bit and calculate the absolute value
  37         of x.
  38         Find out which bit is the highest-set bit. If the number
  39         of that bit <code>> 24</code> then the result has the highest bit
  40         of the mantisse set to one and the exponent equals the
  41         number of the bit + 2. This is due to the fact that we only
  42         have 24 bits for the mantisse.
  43         Otherwise rotate the given integer by
  44         (32 - (number of highes set bit + 1)) bits to the left and
  45         calculate the result from that.
  46
  47 *****************************************************************************/
  48 {
  49     AROS_LIBFUNC_INIT
  50
  51     BYTE Exponent = 0;
  52     LONG TestMask = 0xFFFFFFFF;
  53     LONG Res = 0;
  54
  55     D(kprintf("SPFlt(%d) = ",inum));
  56
  57     if (inum == 0)
  58     {
  59         SetSR(Zero_Bit, Zero_Bit | Negative_Bit | Overflow_Bit);
  60         D(kprintf("0\n"));
  61         return 0;
  62     }
  63
  64     if (inum < 0)
  65     {
  66         Res = FFPSign_Mask;
  67         inum = -inum;
  68     }
  69     /* find out which is the number of the highes set bit */
  70     while (TestMask & inum)
  71     {
  72         Exponent ++;
  73         TestMask <<= 1;
  74     }
  75
  76     /* Exponent = number of highest set bit + 1 */
  77
  78     if (Exponent > 0) /* > 32 bit LONG shift = undefined */
  79         inum <<= (32 - Exponent);
  80     else
  81         inum = 0;
  82     if ((char) inum < 0) inum +=0x100;
  83     inum &= FFPMantisse_Mask;
  84
  85     /* adapt the exponent to the ffp format */
  86     Exponent += 0x40;
  87     Res |= inum | Exponent;
  88     if ((char) Res < 0)
  89     {
  90         SetSR(Negative_Bit, Zero_Bit | Negative_Bit | Overflow_Bit);
  91     }
  92
  93     if (Exponent > (25 + 0x40))
  94     {
  95         Res |= 0x80000000;
  96         SetSR(Overflow_Bit, Zero_Bit | Negative_Bit | Overflow_Bit);
  97     }
  98
  99     D(kprintf("%x\n",Res));
 100
 101     return Res;
 102
 103     AROS_LIBFUNC_EXIT
 104 }