Function should_break_rewrite_pair 

pub fn should_break_rewrite_pair(
    old: &[u8],
    new: &[u8],
    break_score: u64,
) -> bool

Whether an in-place blob edit should be split into delete+create for rename/copy (should_break in diffcore-break.c). break_score is on the internal 0–GIT_DIFF_MAX_SCORE scale (default [DIFF_DEFAULT_BREAK_SCORE]).