将u64中的索引编码为u8。 | 4 bits | 4 bits | | index of nibble | nibble of data | 用法 use crate :: CrumbExt; fn main () { let test: u64 = 0b11111111 ; // let crumb: u8 = unsafe { test.get_unchecked_crumb(1) }; let crumb: u8 = test. get_crumb ( 1 ). unwrap