**Mail Archives: djgpp/1997/05/14/16:39:16**
bshadwick AT juno DOT com (Ben N Shadwick) writes:
> "Angles are represented in a binary format with 256 equal to a full
> circle,
> 64 being a right angle and so on. This has the advantage that a simple
> bitwise 'and' can be used to keep the angle within the range zero to a
> full
> circle, eliminating all those tiresome 'if (angle >= 360)' checks."
>
> Call me stupid, but how exactly would I implement a bitwise and to get it
> to do that (in such a way that it would be more practical than the above
> check)?
const int fixed_point_unit = 0x10000;
const int full_circle = fixed_point_unit * 256;
inline int
clip_angle( int angle )
{
/* This operation becomes a bitwise AND. */
return angle % full_circle;
}
/* Or equivalently... */
inline int
clip_angle( int angle )
{
assert( ( full_circle & ( full_circle - 1 ) ) == 0 );
return angle & ( full_circle - 1 );
}
Tom

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