Unsigned right shift assignment (>>>=)

let a = 5; //   (00000000000000000000000000000101)
a >>>= 2;  // 1 (00000000000000000000000000000001)

let b = -5; // (-00000000000000000000000000000101)
b >>>= 2;   // 1073741822 (00111111111111111111111111111110)