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