Function librsyncr::calculate_signature_with_sizes

pub fn calculate_signature_with_sizes<R: Read, W: Write>(
    old_file: R, 
    sig_file: W, 
    block_size: u32, 
    strong_sum_size: Option<u32>
) -> Result<()>

Calculates the signature file from an old version of a file.

The signature file contains a weak sum and strong sum (currently Blake2b) for each block in the old file.

Using a smaller block_size results in more blocks and a larger signature file. However, with randomly distributed differences, it will also make it more likely that matching blocks can be found when generating the delta file, producing a smaller delta file.

Using a smaller strong_sum_size results in a smaller signature file, but if it is small enough that it results in a collision, then an invalid delta file could be produced that results in a corrupt new file. If None, a default of 32 is used. Using 16 is fine, but you should check the odds of a collision before using smaller than that.