asUintN
BigInt.asUintN(1, 3n) // β 1n
A 1-bit unsigned integer can only represent 0 or 1.
BigInt.asUintN(8, 257n) wraps to 1n because 257 = 256 + 1.
BigInt.asUintN(8, 257n)
1n
Challenge: Verify this wrap.