I'm sorry, but I don't follow. Once the user selected their favorite hash, why would they need to change it in between?
IMO, most users don't care about hashes, and those who do will only want them very occasionally. The fact that they can take significant time to compute means a user might prefer to have them off. The size limit is a workaround for this, but if the hash operation was a separate item, it would be moot: you'd just use it on whatever files you wanted and not need any options.
So all that's left is remove the hash computation altogether?
My preference would be either or both of:
1) A script interface. This would potentially have broader application than just displaying it in the file browser, and a script can use the file_browser function to let the user interactively select files.
2) A simple UI for a single hash function, e.g. a "md5 sum" item in the menu, or a button in the properties dialog (assuming the properties dialog is kept and adding a button isn't too hard)
Since this is a feature with a very small use case, I'd rather keep it to the bare minimum needed to get the desired result (checking a file on the camera matches one elsewhere) or make it a general building block (script).
I must admit that I've gotten the urge to fork CHDK and just implement anything I wanted more than once, courtesy of certain members of this forum.
Which is totally fine if you just want it for yourself. If it's something other people use, you may find this approach becomes unsustainable. In the early days, CHDK had a lot of stuff thrown in because someone thought it was cool, and this has made it a lot harder to maintain in the long run.
