Is any 64-bit portion of a 128-bit hash as collision-proof as a 64-bit hash?
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We're trying to settle an internal debate on our dev team:

We're looking for a 64-bit PHP hash function. We found a [PHP implementation of MurmurHash3](https://github.com/Vaizard/MurmurHash3PHP), but MurmurHash3 is either 32-bit or 128-bit, not 64-bit.

Co-worker #1 believes that to produce a 64-bit hash from MurmurHash3, we can simply slice the first (or last, or any) 64 bits of the 128-bit hash and that it will be as collision-proof as a native 64-bit hash function.

Co-worker #2 believes that we must find a native 64-bit hash function to reduce collisions and that 64-bit slices of a 128-bit hash will not be as collision proof as a native 64-bit hash.

Who's correct?

Does the answer change if we take the first (or last, or any) 64-bits of a cryptographic hash like SHA1 instead of Murmur3?
