* ''fixed AngleDiff(fixed a, fixed b)'' -- returns the shortest signed rotation angle needed to go from angle A to angle B. Result is always in [-0.5, 0.5]. Both A and B may be outside [0.0, 1.0].
  * ''num gcf(num a, num b)'' -- returns the greatest common factor of two numbers.

==== Vector math ====

Since some functions need to return a vector or a pair of angles, they use the ACSUtils [[multiple return values]] convention.

<note important>ZDoom [[zdoom>GetActorPitch]] returns actor pitch with the wrong sign (multiplied by -1). Make sure to fix the sign before using actor pitch in the below vector functions.</note>

Functions returning one value:

  * ''fixed VectorLength3D(fixed x, fixed y, fixed z)'' -- a 3D version of [[zdoom>VectorLength]]. Shorthand for ''VectorLength(z, VectorLength(x, y))''.
  * ''fixed SqVectorLength(fixed x, fixed y)'' -- squared length of 2D vector.
  * ''fixed SqVectorLength3D(fixed x, fixed y, fixed z)'' -- squared length of 3D vector.
  * ''fixed dot2(fixed x1, fixed y1, fixed x2, fixed y2)'' -- dot product of two 2D vectors.
  * ''fixed dot3(fixed x1, fixed y1, fixed z1, fixed x2, fixed y2, fixed z2)'' -- dot product of two 3D vectors.

Functions returning two values:

  * ''fixed, fixed normalize2d(fixed x, fixed y)'' -- returns normalized 2D vector (same direction, but length 1.0)
  * ''fixed, fixed VectorToAngles(fixed x, fixed y, fixed z)'' -- converts vector to a pair of angles (angle and pitch)
  * ''fixed, fixed RotateVector(fixed x, fixed y, fixed angle)'' -- returns vector rotated by angle
  * ''fixed, fixed RotateVectorCS(fixed x, fixed y, fixed rx, fixed ry)'' -- returns vector rotated by another vector's angle. Result is multipled by the second vector's length. If the second vector is normalized, it's a (cos(angle), sin(angle)) vector of rotation angle.
  * ''fixed, fixed RotatePoint(fixed x, fixed y, fixed originX, fixed originY, fixed angle)'' -- returns 2D point rotated by angle around the origin.

Functions returning three values:

  * ''fixed, fixed, fixed normalize3d(fixed x, fixed y, fixed z)'' -- returns normalized 3D vector.
  * ''fixed, fixed, fixed AnglesToVector(fixed angle, fixed pitch)'' -- converts a pair of angles to a vector of length 1.

==== Other useful functions ====

=== mod ===

''num mod(num x, num period)'' -- just like ''x % period'', but performs "true" modulo division, without negative results or mirrorings. It's as if you began at 0 in space [0, period) with wraparound, and moved X steps to the right.

Example of practical use of ''mod'' that wouldn't work with ''%'':

<code>
int NUM_MENU_ITEMS = 10;
int selected_item = 0;

if (KeyPressed(BT_FORWARD))
    selected_item--;
if (KeyPressed(BT_BACK))
    selected_item++;
    
// wrap around
selected_item = mod(selected_item, NUM_MENU_ITEMS);
</code>