Even with git-prime reducing the address space by a few orders of magnitude, there's still (effectively) zero chance for collision. The difference between 10^-29 and 10^-27 isn't that great in practice.

I came here to write that :-)

Actually there are π(N) ~ N / ln(N) primes less than N per the Prime Number Theorem, so π(2 ^ 160) ~ 2 ^ 153.2 - this only drops 7 bits. So that does increase the odds of collision but much less than what I expected!

Maths saved the day again!

I added a section to the README and pages site noting your logic.

It’s ok, you can still assign a unique hash for more than half of the atoms in the universe.