workbench/libs/mathieeesingbas/ieeespfloor.c

   1 /*
   2     Copyright © 1995-2004, The AROS Development Team. All rights reserved.
   3     $Id$
   4 */
   5
   6 #include "mathieeesingbas_intern.h"
   7
   8 /*****************************************************************************
   9
  10     NAME */
  11
  12         AROS_LH1(float, IEEESPFloor,
  13
  14 /*  SYNOPSIS */
  15         AROS_LHA(float, y, D0),
  16
  17 /*  LOCATION */
  18         struct LibHeader *, MathIeeeSingBasBase, 15, Mathieeesingbas)
  19
  20 /*  FUNCTION
  21         Calculate the largest integer ieeesp-number
  22         less than or equal to fnum
  23
  24     INPUTS
  25
  26     RESULT
  27         IEEE single precision floating point
  28
  29         Flags:
  30           zero     : result is zero
  31           negative : result is negative
  32           overflow : 0 (???)
  33
  34     EXAMPLE
  35        IEEESPFloor(10.5) = 10
  36        IEEESPFloor(0.5)  = 0
  37        IEEESPFloor(-0.5) = -1
  38        IEEESPFloor(-10.5)= -11
  39
  40     BUGS
  41
  42     SEE ALSO
  43
  44     INTERNALS
  45
  46 *****************************************************************************/
  47 {
  48     AROS_LIBFUNC_INIT
  49
  50     LONG Mask = 0x80000000;
  51
  52     if (0x7f880000 == y) return y;
  53
  54     if ((y & IEEESPExponent_Mask)  < 0x3f800000)
  55     {
  56         if (y < 0) /* negative sign? */
  57         {
  58             SetSR(Negative_Bit, Zero_Bit | Negative_Bit | Overflow_Bit);
  59             return 0xbf800000; /* -1 */
  60         }
  61         else
  62         {
  63             SetSR(Zero_Bit, Zero_Bit | Negative_Bit | Overflow_Bit);
  64             return 0;
  65         }
  66     }
  67
  68     /* |fnum| >= 1 */
  69     Mask >>= ((y & IEEESPExponent_Mask) >> 23) - 0x77;
  70
  71     /* y is negative */
  72     if (y < 0)
  73     {
  74         /* is there anything behind the decimal dot? */
  75         if (0 != (y & (~Mask)) )
  76         {
  77             y    = IEEESPAdd(y, 0xbf800000 ); /* fnum = fnum -1; */
  78             Mask = 0x80000000;
  79             Mask >>= ((y & IEEESPExponent_Mask) >> 23) - 0x77;
  80         }
  81     }
  82
  83     if(y < 0) SetSR(Negative_Bit, Zero_Bit | Negative_Bit | Overflow_Bit);
  84
  85     return y & Mask;
  86
  87     AROS_LIBFUNC_EXIT
  88 }