private int decode2 (ubyte[] input, ubyte* output)
{
        uint fourbyte, i;
        auto t = _decodeTable.ptr;
        auto dst = output;

        for (ubyte* p=input.ptr, e=p+input.length; p < e; ++p)
            {
            uint v = cast(uint) t[*p];
            if (v || *p == 'A')
               {
               fourbyte = (fourbyte << 8) | v;
               if ((++i & 0x03) is 0)
                  {
                  dst[0] = ((fourbyte << 2)  & 0xff) | ((fourbyte >> 12) & 0x0f);
                  dst[1] = ((fourbyte >> 4)  & 0xf0) | ((fourbyte >> 18) & 0x3f);
                  dst[2] = ((fourbyte >> 18) & 0xc0) | (fourbyte >> 24);
                  fourbyte = 0;
                  dst += 3;
                  }
                }
            }
        return dst - output;
}