workbench/libs/mathtrans/spcos.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 the cosine of a given ffp number in radians
  11
  12     RESULT
  13       Motorola fast floating point number
  14
  15       flags:
  16         zero     : result is zero
  17         negative : result is negative
  18         overflow : 0
  19
  20     NOTES
  21
  22     EXAMPLE
  23
  24     BUGS
  25
  26     SEE ALSO
  27
  28     INTERNALS
  29       Algorithm for Calculation of cos(y):
  30      <code>
  31          z    = floor ( |y| / pi );
  32          y_1  = |y| - z * pi;        => 0 <= y_1 < pi
  33
  34          if (y_1 > pi/2 ) then y_1 = pi - y_1;
  35
  36          => 0 <= y_1 < pi/2
  37
  38          Res = 1 - y^2/2! + y^4/4! - y^6/6! + y^8/8! - y^10/10! =
  39              = 1 -(y^2(-1/2!+y^2(1/4!+y^2(-1/6!+y^2(1/8!-1/10!y^2)))));
  40
  41          if (z was an odd number)
  42            Res = -Res;
  43
  44          if (y_1 was greater than pi/2 in the test above)
  45            Res = -Res;
  46      </code>
  47
  48
  49     HISTORY
  50 */
  51
  52 AROS_LH1(float, SPCos,
  53     AROS_LHA(float, fnum1, D0),
  54     struct Library *, MathTransBase, 7, MathTrans
  55 )
  56 {
  57     AROS_LIBFUNC_INIT
  58
  59     LONG z,Res,ysquared,yabs,tmp;
  60     yabs = fnum1 & (FFPMantisse_Mask + FFPExponent_Mask);
  61
  62     if ((LONG)FFP_Pinfty == yabs)
  63     {
  64         SetSR(Overflow_Bit, Zero_Bit | Negative_Bit | Overflow_Bit);
  65         return FFP_NAN;
  66     }
  67
  68     z = SPFloor(SPDiv(pi, yabs));
  69     tmp  = SPMul(z,pi);
  70     tmp |= FFPSign_Mask; /* tmp = -tmp; */
  71     yabs = SPAdd(yabs, tmp);
  72
  73     if
  74     (
  75             (char)yabs > (char)pio2
  76         &&  (yabs & FFPMantisse_Mask) > (pio2 & FFPMantisse_Mask)
  77     )
  78     {
  79         yabs |= FFPSign_Mask;
  80         yabs  =SPAdd(pi, yabs);
  81         tmp = TRUE;
  82     }
  83     else
  84     {
  85         tmp = FALSE;
  86     }
  87
  88     ysquared = SPMul(yabs,yabs);
  89     Res = SPAdd(cosf1,
  90           SPMul(ysquared,
  91           SPAdd(cosf2,
  92           SPMul(ysquared,
  93           SPAdd(cosf3,
  94           SPMul(ysquared,
  95           SPAdd(cosf4,
  96           SPMul(ysquared,
  97           SPAdd(cosf5,
  98           SPMul(ysquared, cosf6))))))))));
  99
 100     if (0 == Res)
 101     {
 102         SetSR(Zero_Bit, Zero_Bit | Negative_Bit | Overflow_Bit);
 103         return 0;
 104     }
 105
 106     if (TRUE == intern_SPisodd(z)) Res ^= FFPSign_Mask;
 107
 108     if (TRUE == tmp) Res ^= FFPSign_Mask;
 109
 110     if ((char)Res < 0) SetSR(Negative_Bit, Zero_Bit | Negative_Bit | Overflow_Bit);
 111
 112     return Res;
 113
 114     AROS_LIBFUNC_EXIT
 115 }