A CRC-32 checksum implementation for all JavaScript runtimes.

crc32.js

// A CRC32 checksum implementation. It can be used to detect data corruption.
// The 'byte_array' parameter is a Uint8Array, the return value is a signed 32
// bit integer. If you are checksumming a stream of data, pass the last known
// checksum as the 'checksum' parameter.

/*jslint bitwise */

const table = (function () {
    let values = new Int32Array(256);
    let value_nr = 0;
    while (value_nr < 256) {
        let c = value_nr;
        let iteration = 0;
        while (iteration < 8) {
            c = (
                c & 1
                ? 0xEDB88320 ^ (c >>> 1)
                : c >>> 1
            );
            iteration += 1;
        }
        values[value_nr] = c;
        value_nr += 1;
    }
    return values;
}());

function crc32(byte_array, checksum = 0) {
    checksum ^= 0xFFFFFFFF;
    let byte_nr = 0;
    while (byte_nr < byte_array.length) {
        checksum = (checksum >>> 8) ^ table[
            (checksum ^ byte_array[byte_nr]) & 0xFF
        ];
        byte_nr += 1;
    }
    return checksum ^ 0xFFFFFFFF;
}

export default Object.freeze(crc32);