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pub fn int(buf: &[u8]) -> i64 {
    let len = buf.len();
    assert!(len <= 8);
    let mut res: i64 = 0;
    for (i, b) in buf.iter().enumerate() {
        res |= (*b as i64) << (8 * (len - i - 1))
    }
    res
}

#[cfg(test)]
mod tests {
    use super::*;

    #[test]
    fn test_int() {
        for i in 0..=8 {
            assert_eq!(int(&*vec![0u8; i]), 0);
        }
    }
    #[test]
    #[should_panic(expected = "assertion failed: len <= 8")]
    fn test_int_panic() {
        assert_eq!(int(&*vec![0u8; 9]), 0);
    }
}