build = false

[features]
default = ["std"]
rustc-dep-of-std = ["core"]
std = []

[![crates.io](https://img.shields.io/crates/v/adler.svg)](https://crates.io/crates/adler)
[![docs.rs](https://docs.rs/adler/badge.svg)](https://docs.rs/adler/)
![CI](https://github.com/jonas-schievink/adler/workflows/CI/badge.svg)

        const MOD: u32 = 65521;
        const CHUNK_SIZE: usize = 5552 * 4;

        let mut a = u32::from(self.a);
        let mut b = u32::from(self.b);
        let mut a_vec = U32X4([0; 4]);
        let mut b_vec = a_vec;

        let (bytes, remainder) = bytes.split_at(bytes.len() - bytes.len() % 4);

        // iterate over 4 bytes at a time
        let chunk_iter = bytes.chunks_exact(CHUNK_SIZE);
        let remainder_chunk = chunk_iter.remainder();
        for chunk in chunk_iter {
            for byte_vec in chunk.chunks_exact(4) {
                let val = U32X4::from(byte_vec);
                a_vec += val;
                b_vec += a_vec;
            }

            b += CHUNK_SIZE as u32 * a;
            a_vec %= MOD;
            b_vec %= MOD;
            b %= MOD;
        }
        // special-case the final chunk because it may be shorter than the rest
        for byte_vec in remainder_chunk.chunks_exact(4) {
            let val = U32X4::from(byte_vec);
            a_vec += val;
            b_vec += a_vec;
        }
        b += remainder_chunk.len() as u32 * a;
        a_vec %= MOD;
        b_vec %= MOD;
        b %= MOD;

        // combine the sub-sum results into the main sum
        b_vec *= 4;
        b_vec.0[1] += MOD - a_vec.0[1];
        b_vec.0[2] += (MOD - a_vec.0[2]) * 2;
        b_vec.0[3] += (MOD - a_vec.0[3]) * 3;
        for &av in a_vec.0.iter() {
            a += av;
        }
        for &bv in b_vec.0.iter() {
            b += bv;
        }

        // iterate over the remaining few bytes in serial
        for &byte in remainder.iter() {
            a += u32::from(byte);
            b += a;
        }

        self.a = (a % MOD) as u16;
        self.b = (b % MOD) as u16;
    }

#![forbid(unsafe_code)]

#[cfg(feature = "std")]
#[cfg_attr(docsrs, doc(cfg(feature = "std")))]
pub fn adler32<R: BufRead>(mut reader: R) -> io::Result<u32> {
    let mut h = Adler32::new();
    loop {
        let len = {
            let buf = reader.fill_buf()?;
            if buf.is_empty() {
                return Ok(h.checksum());
            }

            h.write_slice(buf);
            buf.len()
        };
        reader.consume(len);
    }
}

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

    #[test]
    fn zeroes() {
        assert_eq!(adler32_slice(&[]), 1);
        assert_eq!(adler32_slice(&[0]), 1 | 1 << 16);
        assert_eq!(adler32_slice(&[0, 0]), 1 | 2 << 16);
        assert_eq!(adler32_slice(&[0; 100]), 0x00640001);
        assert_eq!(adler32_slice(&[0; 1024]), 0x04000001);
        assert_eq!(adler32_slice(&[0; 1024 * 1024]), 0x00f00001);
    }

    #[test]
    fn ones() {
        assert_eq!(adler32_slice(&[0xff; 1024]), 0x79a6fc2e);
        assert_eq!(adler32_slice(&[0xff; 1024 * 1024]), 0x8e88ef11);
    }

    #[test]
    fn mixed() {
        assert_eq!(adler32_slice(&[1]), 2 | 2 << 16);
        assert_eq!(adler32_slice(&[40]), 41 | 41 << 16);

        assert_eq!(adler32_slice(&[0xA5; 1024 * 1024]), 0xd5009ab1);
    }

    /// Example calculation from https://en.wikipedia.org/wiki/Adler-32.
    #[test]
    fn wiki() {
        assert_eq!(adler32_slice(b"Wikipedia"), 0x11E60398);
    }

    #[test]
    fn resume() {
        let mut adler = Adler32::new();
        adler.write_slice(&[0xff; 1024]);
        let partial = adler.checksum();
        assert_eq!(partial, 0x79a6fc2e); // from above
        adler.write_slice(&[0xff; 1024 * 1024 - 1024]);
        assert_eq!(adler.checksum(), 0x8e88ef11); // from above

        // Make sure that we can resume computing from the partial checksum via `from_checksum`.
        let mut adler = Adler32::from_checksum(partial);
        adler.write_slice(&[0xff; 1024 * 1024 - 1024]);
        assert_eq!(adler.checksum(), 0x8e88ef11); // from above
    }

    #[cfg(feature = "std")]
    #[test]
    fn bufread() {
        use std::io::BufReader;
        fn test(data: &[u8], checksum: u32) {
            // `BufReader` uses an 8 KB buffer, so this will test buffer refilling.
            let mut buf = BufReader::new(data);
            let real_sum = adler32(&mut buf).unwrap();
            assert_eq!(checksum, real_sum);
        }

        test(&[], 1);
        test(&[0; 1024], 0x04000001);
        test(&[0; 1024 * 1024], 0x00f00001);
        test(&[0xA5; 1024 * 1024], 0xd5009ab1);
    }
}

#![doc(html_root_url = "https://docs.rs/adler2/2.0.0")]