Content-based Fingerprinting

Source and derived files are identified by a 128-bit fingerprint for dependency analysis
- A fingerprint is essentially a checksum of the files contents
- If a source has not changed or is edited back to be identical to any previous version, both the repository and the build system know.
- If a result file (e.g. an object file produced by a compiler) is identical to any previous one, the build system knows.

Source and derived files are identified by a 128-bit fingerprint for dependency analysis