Takes parameters and converts them to 64 bit integers, then returns the unsigned 64 bit XOR of those two values. If either value is NULL then the result is NULL.
Example:
SELECT xor('1234567890', '9876543210', 9876543210)
returns 1234567890
SELECT xor('1234567890', '9876543210')
returns 8676316216
SELECT xor('1234567890')
returns 0
SELECT xor()
returns SYNTAX ERROR