Tool to scan files for common byte sequences

[chants]

Grep is just looking for regex's so its complexity is that of pattern matching of regex's. Now you are asking a very general and arbitrary common substring problem. They are not the same issue really at all.

This would be very useful, but it has a really problematic size vs speed tradeoff and would need some kind of limiting parameters like you are getting at. The NP-hard issue can be side stepped through heuristics and domain specific approach. Nonetheless, I doubt you will find such a tool for general cases.