Test comparing Nan using FPC

uses Math, CastleVectors;
var
  F, F2, F3: Single;
begin
  F := Nan;
  F2 := Nan;

  { Doing some operations on Nan values produces "Invalid floating point operation".
    (Unless the FPU exceptions are masked out. Which happens to be always true when
    a program uses OpenGL, FPC GL unit has to mask out exceptions to protect from
    OpenGL implementations producing FPU errors.)
    So below we  explicitly silence them by Math.ClearExceptions(false). }

  Writeln(F = F2); // true
  Math.ClearExceptions(false);

  Writeln(FloatsEqual(F, F2)); // false (reason explained below)
  Math.ClearExceptions(false);

  F3 := F - F2; // Nan, because subtracting Nans is Nan
  Math.ClearExceptions(false);
  Writeln(F3);

  F3 := Abs(F3); // Nan, because Abs(Nan) is Nan
  Math.ClearExceptions(false);
  Writeln(F3);

  Writeln(F3 < 0.1); // false, because comparing using < or > normal number with Nan is false
  Math.ClearExceptions(false);
end.