If that mechanical process is not reversible, then it's not a copyright violation. For instance, I can compute the SHA256 hashes for every book in existence and distribute the resulting table of (ISBN, SHA256) and that is not a copyright violation.
That's actually within the other fair use factors. So your hash table is fair use because its transformative and doesn't substitute for the original work.
It's actually even less than fair use, it's non-copyright use: one-way hashes are intentionally designed to eliminate the creative element and output random looking data.
