basalt-db 0.1.5

/// Hand-rolled CRC-32 (ISO-HDLC / IEEE 802.3, polynomial 0xEDB88320),
/// table-driven. Used for WAL frame checksums.
const CRC_TABLE: [u32; 256] = make_crc_table();

const fn make_crc_table() -> [u32; 256] {
    let mut table = [0u32; 256];
    let mut i = 0usize;
    while i < 256 {
        let mut c = i as u32;
        let mut k = 0;
        while k < 8 {
            c = if c & 1 != 0 {
                0xEDB8_8320 ^ (c >> 1)
            } else {
                c >> 1
            };
            k += 1;
        }
        table[i] = c;
        i += 1;
    }
    table
}

pub fn crc32(bytes: &[u8]) -> u32 {
    let mut crc: u32 = 0xFFFF_FFFF;
    for &b in bytes {
        crc = CRC_TABLE[((crc ^ b as u32) & 0xFF) as usize] ^ (crc >> 8);
    }
    crc ^ 0xFFFF_FFFF
}

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

    #[test]
    fn known_vectors() {
        // Standard CRC-32 test vectors.
        assert_eq!(crc32(b""), 0x0000_0000);
        assert_eq!(crc32(b"123456789"), 0xCBF4_3926);
    }

    #[test]
    fn detects_bit_flips() {
        let a = crc32(b"the quick brown fox");
        let mut mangled = b"the quick brown fox".to_vec();
        mangled[5] ^= 0x40;
        assert_ne!(a, crc32(&mangled));
    }
}