workbench/libs/mathtrans/spatan.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       Calculates the angle of a given number representing the tangent
  11       of that angle. The angle will be in radians.
  12
  13     RESULT
  14       Motorola fast floating point number
  15
  16     NOTES
  17
  18     EXAMPLE
  19
  20     BUGS
  21
  22     SEE ALSO
  23
  24     INTERNALS
  25
  26     HISTORY
  27 */
  28
  29 AROS_LH1(float, SPAtan,
  30     AROS_LHA(float, fnum1, D0),
  31     struct Library *, MathTransBase, 5, MathTrans
  32 )
  33 {
  34     AROS_LIBFUNC_INIT
  35
  36     LONG fnumabs = fnum1 & (FFPMantisse_Mask | FFPExponent_Mask);
  37     LONG fnumsquared, fnumcubed;
  38
  39     /* check for +- infinity -> output: +-pi/2 */
  40     if ((LONG)FFP_Pinfty == fnumabs ) return (pio2 | (fnum1 & FFPSign_Mask));
  41
  42     /* atan(0) = 0 */
  43     if (0 == fnumabs)
  44     {
  45         SetSR(Zero_Bit, Zero_Bit | Negative_Bit | Overflow_Bit);
  46         return 0;
  47     }
  48
  49     /* atan(x>= 128) = pi/2 - 1/x */
  50     if ((BYTE) fnumabs >= 0x48)
  51     {
  52         if (fnumabs == fnum1) /* arg has ppositive sign */
  53         {
  54             SetSR(0, Zero_Bit | Negative_Bit | Overflow_Bit);
  55             return SPSub(SPDiv(fnumabs,one),pio2);
  56         }
  57         else
  58         {
  59             LONG res;
  60             SetSR(Negative_Bit, Zero_Bit | Negative_Bit | Overflow_Bit);
  61
  62             /* workaround a bug in egcs 1.0.3: complains about illegal operands to | */
  63             res = SPSub(SPDiv(fnumabs,one),pio2);
  64             return res | FFPSign_Mask;
  65         }
  66     }
  67
  68     /* atan(x >= 64) = pi/2 - 1/x +1/(3*x^3) */
  69
  70     fnumsquared = SPMul(fnumabs, fnumabs);
  71
  72     if((BYTE) fnumabs >= 0x47)
  73     {
  74         fnumcubed   = SPMul(fnumabs, fnumsquared);
  75
  76         /* pi/2 - 1/x + 1/(3*x^3) = pi/2 + (1-3*x^2)/(3*x^3)*/
  77         if (fnumabs == fnum1) /* arg has positive sign */
  78         {
  79             LONG res;
  80             SetSR(0, Zero_Bit | Negative_Bit | Overflow_Bit);
  81
  82             /* workaround a bug in egcs 1.0.3: complains about illegal operands to | */
  83             res = SPMul(three, fnumsquared);
  84             return SPAdd
  85             (
  86                 pio2, SPDiv
  87                 (
  88                     SPMul(three, fnumcubed),
  89                     SPAdd(res | FFPSign_Mask, one)
  90                 )
  91             );
  92         }
  93         else
  94         {
  95             LONG res;
  96             SetSR(Negative_Bit, Zero_Bit | Negative_Bit | Overflow_Bit);
  97
  98             /* workaround a bug in egcs 1.0.3: complains about illegal operands to | */
  99             res = SPMul(three, fnumsquared);
 100             res = SPAdd
 101             (
 102                 pio2, SPDiv
 103                 (
 104                     SPMul(three, fnumcubed),
 105                     SPAdd( res | FFPSign_Mask, one )
 106                 )
 107             );
 108             return res | FFPSign_Mask;
 109         }
 110     }
 111
 112     /* atan(x <= 64) */
 113     return SPAsin(SPDiv(SPSqrt(SPAdd(one,fnumsquared)),fnum1));
 114
 115     AROS_LIBFUNC_EXIT
 116 }