I guess you could use fewer magic numbers if you want, for example instead of:

  proc createCRCTable(): array[256, CRC32] =
    for i in 0..255:

You can write:

  proc createCRCTable(): array[256, CRC32] =
    for i in result.low .. result.high:

Or:

  proc createCRCTable(): array[256, CRC32] =
    for i, v in result: # index, value

Or define your own indices iterator:

  iterator indices(x) =
    for i in x.low .. x.high:
      yield i

  proc createCRCTable(): array[256, CRC32] =
    for i in result.indices:

I think I should propose adding indices to the standard library.