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    pub const CASTAGNOLI: u32 = 0x82f63b78;
    pub const IEEE: u32 = 0xedb88320;
    pub const KOOPMAN: u32 = 0xeb31d82e;

    lazy_static! {
        pub static ref IEEE_TABLE: [u32; 256] = make_table(IEEE);
        pub static ref CASTAGNOLI_TABLE: [u32; 256] = make_table(CASTAGNOLI);
        pub static ref KOOPMAN_TABLE: [u32; 256] = make_table(KOOPMAN);
    }

    pub struct Digest {
        table: [u32; 256],
        initial: u32,
        value: u32
    }

    pub trait Hasher32 {
        fn reset(&mut self);
        fn write(&mut self, bytes: &[u8]);
        fn sum32(&self) -> u32;
    }

    pub fn make_table(poly: u32) -> [u32; 256] {
        let mut table = [0u32; 256];
        for i in 0..256 {
            let mut value = i as u32;
            for _ in 0..8 {
                value = if (value & 1) == 1 {
                    (value >> 1) ^ poly
                } else {
                    value >> 1
                }
            }
            table[i] = value;
        }
        table
    }

    pub fn update(mut value: u32, table: &[u32; 256], bytes: &[u8]) -> u32 {
        value = !value;
        for &i in bytes.iter() {
            value = table[((value as u8) ^ i) as usize] ^ (value >> 8)
        }
        !value
    }

    pub fn checksum_ieee(bytes: &[u8]) -> u32 {
        return update(0, &IEEE_TABLE, bytes);
    }

    pub fn checksum_castagnoli(bytes: &[u8]) -> u32 {
        return update(0, &CASTAGNOLI_TABLE, bytes);
    }

    pub fn checksum_koopman(bytes: &[u8]) -> u32 {
        return update(0, &KOOPMAN_TABLE, bytes);
    }

    impl Digest {
        pub fn new(poly: u32) -> Digest {
            Digest {
                table: make_table(poly),
                initial: 0,
                value: 0
            }
        }

        pub fn new_with_initial(poly: u32, initial: u32) -> Digest {
            Digest {
                table: make_table(poly),
                initial: initial,
                value: initial
            }
        }
    }

    impl Hasher32 for Digest {
        fn reset(&mut self) {
            self.value = self.initial;
        }
        fn write(&mut self, bytes: &[u8]) {
            self.value = update(self.value, &self.table, bytes);
        }
        fn sum32(&self) -> u32 {
            self.value
        }
    }

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