Rabin Fingerprinting is one of my favorites of his contributions. It's a "rolling hash" that allows you to quickly compute a 32-bit (or larger) hash at *every* byte offset of a file. It is used most notably to do file block matching/deduplication when those matching blocks can be at any offset. It's tragically underappreciated.
I've been meaning to write up a tutorial as part of my Galois Field series. Someday..
Thank you again!
This replaced some O(n²) searches through ASCII text, reducing search time from dozens of seconds to fractions of a second.
0 - https://github.com/ttkb-oss/mipsmatch 1 - https://github.com/ttkb-oss/mipsmatch/wiki/Identifiers
I especially like how if you end up with hash characteristics that you don't like, your can just select a different irreducible Galois polynomial and now you've got a whole new hash algorithm. It's like tuning to a different frequency.
For me it means I don't have to worry about cases where there aren't enough nearby fingerprints for the annotation to adhere to, I can just add or remove polynomials until I get a good density.
I wrote a Rabin—Karp implementation in ~2006 as part of the spam and threat scanning stack for the MX Logic mail service. It was incredibly performant, letting us test {n} bytes against an essentially unlimited number of string signatures in O(n) time.