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auto_arc_tan() version 5
Integer Version (using an arc tangent look-up table). See version 1 for more information.
// N.B. There is a 16 bit version of this routine below this one.
long auto_arc_tan( long v_dx, long v_dy )
{
// AUTOMATIC ARC TANGENT ROUTINE returning an Signed 32 bit value.
// (c) Jon P
//
// Version 5.0 Speed-up routine with a look-up table rather than a formula.
//
#define ARC_TANGENT_TABLE_SIZE 129
#define ARC_TANGENT_ONE 512
static unsigned char arc_tangent_table[ ARC_TANGENT_TABLE_SIZE ] =
{
0, 1, 2, 3, 4, 5, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16,
17, 18, 19, 20, 21, 22, 23, 24, 25, 26, 27, 28, 28, 29, 30, 31,
32, 32, 33, 34, 35, 35, 36, 37, 37, 38, 39, 39, 40, 40, 41, 41,
42, 42, 43, 43, 44, 44, 44, 45, 45, 45, 45, 46, 46, 46, 46, 46,
46, 46, 46, 46, 46, 46, 46, 46, 46, 46, 46, 46, 45, 45, 45, 44,
44, 44, 43, 43, 43, 42, 42, 41, 41, 40, 39, 39, 38, 38, 37, 36,
35, 35, 34, 33, 32, 31, 31, 30, 29, 28, 27, 26, 25, 24, 23, 22,
21, 19, 18, 17, 16, 15, 14, 12, 11, 10, 8, 7, 6, 4, 3, 1,
0
}; // ...This array was made by ATAN_TBL.BAS JonP
register long grad, ang, abs_dx, abs_dy, half;
abs_dx = v_dx;
if ( abs_dx < 0 ) abs_dx = 0 - abs_dx;
abs_dy = v_dy;
if ( abs_dy < 0 ) abs_dy = 0 - abs_dy;
// find the gradient between 0 and "1 in 1" (or 0 and 512 in this impelmentation)....
if ( abs_dy <= abs_dx )
{
if ( abs_dx == 0 )
{ //exact angle can be returned... also this prevents divide by 0 error...
if ( v_dy >= 0 )
return 0;
else
return 2048;
}
grad = abs_dy;
grad <<= 9;
grad /= abs_dx;
half = 1;
}
else
{
if ( abs_dy == 0 )
{ //exact angle can be returned... also this prevents divide by 0 error...
if ( v_dx >= 0 )
return 1024;
else
return 3072;
}
grad = abs_dx;
grad <<= 9;
grad /= abs_dy;
half = 0;
}
// We now have a gradient between 0 and "1 in 1" (0 to 512).
// Access the arc tangent look-up table to convert the gradient to
// an angle between 0 and 45 degrees (0 to 512)...
ang = arc_tangent_table[grad>>2] + grad;
if ( v_dx >= 0 )
{
if ( v_dy >= 0 )
{
if ( half ) ang = 1024 - ang;
}
else
{
if ( half )
ang += 1024;
else
ang = 2048 - ang;
}
}
else
{
if ( v_dy >= 0 )
{
if ( half )
ang += 3072;
else
ang = 4096 - ang;
}
else
{
if ( half )
ang = 3072 - ang;
else
ang += 2048;
}
}
// The next line is for testing only....
// printf( "\ndx %d dy %d = ang %d ", v_dx, v_dy, ang );
return ang;
}
short auto_arc_tan_s16( long v_dx, long v_dy )
{
// AUTOMATIC ARC TANGENT ROUTINE returning an Signed 16 bit value.
// (c) Jon P
//
// Version 5.0 Speed-up routine with a look-up table rather than a formula.
//
#define ARC_TANGENT_TABLE_SIZE 129
#define ARC_TANGENT_ONE 512
static unsigned char arc_tangent_table[ ARC_TANGENT_TABLE_SIZE ] =
{
0, 1, 2, 3, 4, 5, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16,
17, 18, 19, 20, 21, 22, 23, 24, 25, 26, 27, 28, 28, 29, 30, 31,
32, 32, 33, 34, 35, 35, 36, 37, 37, 38, 39, 39, 40, 40, 41, 41,
42, 42, 43, 43, 44, 44, 44, 45, 45, 45, 45, 46, 46, 46, 46, 46,
46, 46, 46, 46, 46, 46, 46, 46, 46, 46, 46, 46, 45, 45, 45, 44,
44, 44, 43, 43, 43, 42, 42, 41, 41, 40, 39, 39, 38, 38, 37, 36,
35, 35, 34, 33, 32, 31, 31, 30, 29, 28, 27, 26, 25, 24, 23, 22,
21, 19, 18, 17, 16, 15, 14, 12, 11, 10, 8, 7, 6, 4, 3, 1,
0
}; // ...This array was made by ATAN_TBL.BAS JonP
register long grad, abs_dx, abs_dy, half;
register short ang;
abs_dx = v_dx;
if ( abs_dx < 0 ) abs_dx = 0 - abs_dx;
abs_dy = v_dy;
if ( abs_dy < 0 ) abs_dy = 0 - abs_dy;
// find the gradient between 0 and "1 in 1" (or 0 and 512 in this impelmentation)....
if ( abs_dy <= abs_dx )
{
if ( abs_dx == 0 )
{ //exact angle can be returned... also this prevents divide by 0 error...
if ( v_dy >= 0 )
return 0;
else
return 2048;
}
grad = abs_dy;
grad <<= 9;
grad /= abs_dx;
half = 1;
}
else
{
if ( abs_dy == 0 )
{ //exact angle can be returned... also this prevents divide by 0 error...
if ( v_dx >= 0 )
return 1024;
else
return 3072;
}
grad = abs_dx;
grad <<= 9;
grad /= abs_dy;
half = 0;
}
// We now have a gradient between 0 and "1 in 1" (0 to 512).
// Access the arc tangent look-up table to convert the gradient to
// an angle between 0 and 45 degrees (0 to 512)...
ang = arc_tangent_table[grad>>2] + grad;
if ( v_dx >= 0 )
{
if ( v_dy >= 0 )
{
if ( half ) ang = 1024 - ang;
}
else
{
if ( half )
ang += 1024;
else
ang = 2048 - ang;
}
}
else
{
if ( v_dy >= 0 )
{
if ( half )
ang += 3072;
else
ang = 4096 - ang;
}
else
{
if ( half )
ang = 3072 - ang;
else
ang += 2048;
}
}
// The next line is for testing only....
// printf( "\ndx %d dy %d = ang %d ", v_dx, v_dy, ang );
return ang;
}