Provide a concise functional overview of the code excerpt mentioned below

procedure f(var A : array of integer; L, R: Integer);
var
 I, J: Integer;
 P, T: Integer;
begin
 repeat
 I := L;
 J := R;
 P := A[(L + R) shr 1];
 repeat
 while A[I] < P do
 Inc(I);
 while A[J] > P do
 Dec(J);
 if I <= J then
 begin
 T := A[I];
 A[I] := A[J];
 A[J] := T;
 Inc(I);
 Dec(J);
 end;
 until I > J;
 if L < J then
 f(A, L, J);
 L := I;
 until I >= R;
end;
Question 2
procedure f( var a : integer; var b : integer );
begin
 a := a xor b;
 b := a xor b;
 a := a xor b;
end;