Is there a function to shift degrees of a circle past 0?

Question

I'm looking for a function somewhere in Delphi XE2 similar to Inc() which allows me to add/subtract a number of degrees from a current number of degrees and result in the new degrees. For example, if I have a point currently at 5 degrees around a circle, and I want to subtract 10, I should not get -5 degrees, but rather 355 (360 - 5). Same as adding past 360 - it should go back to 0 when it reaches 360.

Is there anything like this already in Delphi so I don't have to re-write it? Perhaps in the Math unit?

Answer 1

uses
  System.SysUtils,Math;

Function WrapAngle( angle : Double) : Double;
Const
  modAngle : Double = 360.0;
begin
  Result := angle - modAngle*Floor(angle/modAngle);
end;

begin
  WriteLn(FloatToStr(WrapAngle(-5)));
  WriteLn(FloatToStr(WrapAngle(5-720)));
  WriteLn(FloatToStr(WrapAngle(360)));
  ReadLn;    
end.

Produces result:

355
5 
0

Update:

As @Giel found, in XE3 there is a new function DegNormalize() which does the job. Even about 25% faster. The trick is to replace the Floor() call with an Int() instead, and if the result is negative, add modAngle to the result.