src/crc.rs

#![cfg(feature = "gzip")]

use crate::crc::crc_tables::{CRC32_SLICE1_TABLE, CRC32_SLICE8_TABLE};

mod crc_tables;

/// Calculate crc for a data and an initial crc value
#[allow(clippy::identity_op, clippy::zero_prefixed_literal)]
pub fn crc32(data: &[u8], mut crc: u32) -> u32
{
    // main loop
    for chunk in data.chunks_exact(8)
    {
        let chunk_loaded = u64::from_le_bytes(chunk.try_into().unwrap());

        let v1 = (chunk_loaded & u64::from(u32::MAX)) as u32;
        let v2 = (chunk_loaded >> 32) as u32;

        crc = CRC32_SLICE8_TABLE[0x700 + (((crc ^ v1) >> 00) & 0xFF) as usize]
            ^ CRC32_SLICE8_TABLE[0x600 + (((crc ^ v1) >> 08) & 0xFF) as usize]
            ^ CRC32_SLICE8_TABLE[0x500 + (((crc ^ v1) >> 16) & 0xFF) as usize]
            ^ CRC32_SLICE8_TABLE[0x400 + (((crc ^ v1) >> 24) & 0xFF) as usize]
            ^ CRC32_SLICE8_TABLE[0x300 + (((v2 >> 00) & 0xFF) as usize)]
            ^ CRC32_SLICE8_TABLE[0x200 + (((v2 >> 08) & 0xFF) as usize)]
            ^ CRC32_SLICE8_TABLE[0x100 + (((v2 >> 16) & 0xFF) as usize)]
            ^ CRC32_SLICE8_TABLE[0x000 + (((v2 >> 24) & 0xFF) as usize)];
    }
    // handle remainder
    for remainder in data.chunks_exact(8).remainder()
    {
        crc = (crc >> 8) ^ CRC32_SLICE1_TABLE[((crc & 0xFF) ^ u32::from(*remainder)) as usize];
    }

    crc
}