gamma code in Rust

gamma.rs

// https://crates.io/crates/bit-vec
use bit_vec::BitVec;

pub fn encode_gamma(li: &[usize]) -> BitVec {
    fn encode(k: usize) -> BitVec {
        let body_len: usize = ((k as f64).log2().floor() as usize) + 1;
        let body = BitVec::from_bytes(&k.to_be_bytes());

        let mut bv = BitVec::from_elem(body_len * 2 - 1, false);
        // set selector bit
        bv.set(body_len - 1, true);
        // set body bits
        let mut pos = body_len;
        let mut i = body.len() - body_len + 1;
        while pos < bv.len() {
            if let Some(b) = body.get(i) {
                bv.set(pos, b);
            }
            pos += 1;
            i += 1;
        }
        bv
    }

    let mut bv_all = BitVec::new();
    for &k in li {
        let bv = encode(k);
        let mut offset = bv_all.len();
        bv_all.grow(bv.len(), false);
        for bit in bv.iter() {
            bv_all.set(offset, bit);
            offset += 1;
        }
    }
    bv_all
}