[Scons-users] hashing + decider question

[Robert Zeigler]

I'm interested in implementing a decider that hashes only a portion of a file's contents. As far as I can tell from docs and code, doing this would either require:
1) I manage the cached hash state myself, external to scons' built-in hashing support 
or
2) I fork scons and override the hashing functionality in Util.py

I know I can supply my own decider, but if I attempt to get the csig for dependencies, it's going to call, eventually, into MD5filesignature, which wants to hash the entire file.

Is there some way I'm missing to provide a custom signature strategy?

Thanks,

Robert