question: public int check_prefix ( final byte [ ] key , int depth ) { int max_cmp = Math . min ( Math . min ( partial_len , Node . MAX_PREFIX_LEN ) , key . length - depth ) ; int idx ; for ( idx = 0 ; idx < max_cmp ; idx ++ ) { if ( partial [ idx ] != key [ depth + idx ] ) return idx ; } return idx ; }
target:  Returns the number of prefix characters shared between the key and node.