webmail/lib/mail-export/crc32.ts

let table: Uint32Array | null = null;

function crcTable(): Uint32Array {
  if (table) return table;
  table = new Uint32Array(256);
  for (let n = 0; n < 256; n++) {
    let c = n;
    for (let k = 0; k < 8; k++) c = c & 1 ? 0xedb88320 ^ (c >>> 1) : c >>> 1;
    table[n] = c >>> 0;
  }
  return table;
}

/** CRC-32 (ZIP, PNG) of `data`, continuing from `crc` for streamed input. */
export function crc32(data: Uint8Array, crc = 0): number {
  const t = crcTable();
  let c = (crc ^ 0xffffffff) >>> 0;
  for (let i = 0; i < data.length; i++) c = t[(c ^ data[i]) & 0xff] ^ (c >>> 8);
  return (c ^ 0xffffffff) >>> 0;
}