[ccache] BSDiff for cache objects

[Jürgen Buchmüller]

Am Montag, den 12.11.2012, 13:49 +0200 schrieb Bogdan Harjoc:
> Basically, before writing a new object file, ccache could find a similar
> object in the cache (based on object-code or source-code hashes for
> example)

The main goal of most hashes is to give very distinct results even for
even small changes in the input data, which is why there is not really
an algorithm to compare two files' similarity based on hashes.

Similarity of two files would have to be calculated based on something
that currently isn't available - AFAICT. The savings in size are
probably less important than the expectable performance loss for
building deltas of source and/or object files.

Juergen