function adler32(adler, buf, len, pos) {
  var s1 = (adler & 0xffff) |0
    , s2 = ((adler >>> 16) & 0xffff) |0
    , n = 0;

  while (len !== 0) {
    // Set limit ~ twice less than 5552, to keep
    // s2 in 31-bits, because we force signed ints.
    // in other case %= will fail.
    n = len > 2000 ? 2000 : len;
    len -= n;

    do {
      s1 = (s1 + buf[pos++]) |0;
      s2 = (s2 + s1) |0;
    } while (--n);

    s1 %= 65521;
    s2 %= 65521;
  }

  return (s1 | (s2 << 16)) |0;
}
ungzip(data[, options]) -> Uint8Array|Array|String
- data (Uint8Array|Array|String): input data to compress.
- options (Object): zlib inflate options.

Just shortcut to [[inflate]], because it autodetects format
by header.content. Done for convenience.