Convert Rust u8 slice to i32

slice_to_i32.rs

fn slice_to_i32_be(data: &[u8]) -> i32 {
    assert!(data.len() >= 4);
    let first = data[0];
    let sign = if first & 0x80 != 0 { -1 } else { 1 };
    sign * (
        (((first & 0x7F) as i32) << 24) +
        ((data[1] as i32)        << 16) +
        ((data[2] as i32)        << 8 ) +
        ( data[3] as i32              )
    )
}

fn slice_to_i32_le(data: &[u8]) -> i32 {
    assert!(data.len() >= 4);
    let first = data[3];
    let sign = if first & 0x80 != 0 { -1 } else { 1 };
    sign * (
        (((first & 0x7F) as i32) << 24) +
        ((data[2] as i32)        << 16) +
        ((data[1] as i32)        << 8 ) +
        ( data[0] as i32              )
    )
}