compresses datetime into 2 bytes

datetime_to_2bytes.cs

  // represent the full date w/ 16 bits (2 bytes)
  //
  // d - day
  // m - month
  // y - year
  //
  /// format:
  // d d d d d | m m m m | y y y y y y y
  //
  // 5 bits to represent the day   - 2^5 = 32
  // 4 bits to represent the month - 2^4 = 16
  // 7 bits to represent the year  - 2^7 = 128, we use only the last 2 digits
  // and support the year range from 2000 to 2099
  var b_year = new BitArray(7);
  var b_mnth = new BitArray(4);
  var b_days = new BitArray(5);
  var b_dt = new BitArray(16);

  var dates = new List<DateTime>
  {
    DateTime.Now,
    DateTime.Now.AddYears(7),
    DateTime.Now.AddYears(-4)
  };

  byte i = 0, offset = 0;
  byte[] bytes = new byte[4];
  BitArray bits = null;
  foreach (var dt in dates)
  {
    // clear
    b_dt.SetAll(false);
    b_days.SetAll(false);
    b_mnth.SetAll(false);
    b_year.SetAll(false);

    // convert days to 5-bit array
    bytes = BitConverter.GetBytes(dt.Day);
    bits = new BitArray(bytes);
    for (i = 0; i < 8; ++i)
    {
      if (i == b_days.Length)
        break;

      b_days.Set(i, bits[i]);
    }

    // convert months to 4-bit array
    bytes = BitConverter.GetBytes(dt.Month);
    bits = new BitArray(bytes);
    for (i = 0; i < 8; ++i)
    {
      if (i == b_mnth.Length)
        break;

      b_mnth.Set(i, bits[i]);
    }

    // convert years to 7-bit array
    bytes = BitConverter.GetBytes(Convert.ToByte(dt.Year.ToString().Substring(2, 2)));
    bits = new BitArray(bytes);
    for (i = 0; i < 8; ++i)
    {
      if (i == b_year.Length)
        break;

      b_year.Set(i, bits[i]);
    }

    // glue together
    for (i = 0; i < b_days.Length; ++i)
      b_dt.Set(i, b_days[i]);

    offset = i;
    for (i = 0; i < b_mnth.Length; ++i)
      b_dt.Set(i + offset, b_mnth[i]);

    offset = i;
    for (i = 0; i < b_year.Length; ++i)
      b_dt.Set(i + offset, b_year[i]);
  }