rom/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     FUNCTION
  10
  11     RESULT
  12         FFP number
  13
  14         Flags:
  15           zero     : result is zero
  16           negative : result is negative
  17           overflow : ffp is not exactly the integer
  18
  19     NOTES
  20
  21     EXAMPLE
  22
  23     BUGS
  24
  25     SEE ALSO
  26
  27     INTERNALS
  28         Return zero for x == 0.<br/>
  29         If <code>x < 0</code> set the sign-bit and calculate the absolute value
  30         of x.<br/>
  31         Find out which bit is the highest-set bit. If the number
  32         of that bit <code>> 24</code> then the result has the highest bit
  33         of the mantisse set to one and the exponent equals the
  34         number of the bit + 2. This is due to the fact that we only
  35         have 24 bits for the mantisse.
  36         Otherwise rotate the given integer by
  37         <code>(32 - (number of highes set bit + 1))</code> bits to the left and
  38         calculate the result from that.
  39
  40     HISTORY
  41
  42 */
  43
  44 AROS_LH1(float, SPFlt,
  45     AROS_LHA(LONG, inum, D0),
  46     struct LibHeader *, MathBase, 6, Mathffp
  47 )
  48 {
  49     AROS_LIBFUNC_INIT
  50
  51     BYTE Exponent = 0;
  52     LONG TestMask = 0xFFFFFFFF;
  53     LONG Res = 0;
  54
  55     kprintf("SPFlt(%d)=",inum);
  56
  57     if (inum == 0)
  58     {
  59         SetSR(Zero_Bit, Zero_Bit | Negative_Bit | Overflow_Bit);
  60         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     inum <<= (32 - Exponent);
  79     if ((char) inum < 0) inum +=0x100;
  80     inum &= FFPMantisse_Mask;
  81
  82     /* adapt the exponent to the ffp format */
  83     Exponent += 0x40;
  84     Res |= inum | Exponent;
  85     if ((char) Res < 0)
  86     {
  87         SetSR(Negative_Bit, Zero_Bit | Negative_Bit | Overflow_Bit);
  88     }
  89
  90     if (Exponent > (25 + 0x40))
  91     {
  92         Res |= 0x80000000;
  93         SetSR(Overflow_Bit, Zero_Bit | Negative_Bit | Overflow_Bit);
  94     }
  95
  96     kprintf("%x\n",Res);
  97
  98     return Res;
  99
 100     AROS_LIBFUNC_EXIT
 101 }