Returns a**e unless e <= 0 (in which case returns 1).

Returns x << n.

MustFromString convers dec string into big integer and panics if conversion is not sucessful.

PositiveFromUnsignedBytes interprets b as the bytes of a big-endian unsigned integer and returns a positive Int with this absolute value.

Returns x >> n.

BigIntMaxSerializedLen is the max length of a byte slice representing a CBOR serialized big.