It's a custom hash function. Like most other home-brewn hash functions it has serious flaws for this use. This is a reason you see many hash collisions.
Another reason is simply the fact that the output is as short as 64 bits. Regardless of the quality of a hash function, if it has n bits of output it is simply bound to have at least one hash collision for 2â¿+1 inputs.
Another reason is simply the fact that the output is as short as 64 bits. Regardless of the quality of a hash function, if it has n bits of output it is simply bound to have at least one hash collision for 2â¿+1 inputs.