LEB128 VarInt decoding

leb128.rs

const HIGH_BIT: u8 = 0b10000000;
fn hi_bit_set(byte: u8) -> bool {
    byte & HIGH_BIT != 0
}

pub fn naive(buf: &mut &[u8]) -> Result<u64, ()> {
    let mut value = 0;
    let mut iter = buf.iter();
    for (count, &byte) in (&mut iter).enumerate().take(10) {
        value += u64::from(byte & !HIGH_BIT) << (count * 7);
        if !hi_bit_set(byte) {
            *buf = iter.as_slice();
            return Ok(value);
        }
    }
    Err(())
}

Typical implementations will optimize the algorithm, generally making up 40% in performance. Common tricks check the first byte for the HIGH_BIT, and elide bounds checks by checking the length up front