VarInt.cs

public static class VarInt {
  public static bool TryRead(ReadOnlySpan < byte > slice, out int value, out int readBytes) {
    readBytes = 0;
    value = 0;
    var shift = 0;
    while (true) {
      if (readBytes >= slice.Length)
        return false;

      var nextByte = slice[readBytes++];

      var meanBits = nextByte & 0b0111_1111;
      value |= meanBits << shift;

      var highBit = nextByte & 0b1000_0000;
      var noMoreBytes = highBit == 0;
      if (noMoreBytes)
        return true;

      shift += 7;
    }
  }

  public static int GetSize(int value) {
    var val = (uint) value;
    var count = 0;
    do {
      val >>= 7;
      count++;
    } while (val != 0);

    return count;
  }

  public static int Write(Span < byte > slice, int value) {
    var val = (uint) value;
    var written = 0;
    do {
      var temp = (byte)(val & 0b01111111);
      val >>= 7;
      if (val != 0) {
        temp |= 0b10000000;
      }

      slice[written++] = temp;
    } while (val != 0);

    return written;
  }
}

public static class VarLong {
  public static bool TryRead(ReadOnlySpan < byte > slice, out long value, out int readBytes) {
    readBytes = 0;
    value = 0;
    var shift = 0;
    while (true) {
      if (readBytes >= slice.Length)
        return false;

      var nextByte = slice[readBytes++];

      long meanBits = nextByte & 0b0111_1111;
      value |= meanBits << shift;

      var highBit = nextByte & 0b1000_0000;
      var noMoreBytes = highBit == 0;
      if (noMoreBytes)
        return true;

      shift += 7;
    }
  }

  public static int GetSize(long value) {
    var val = (uint) value;
    var count = 0;
    do {
      val >>= 7;
      count++;
    } while (val != 0);

    return count;
  }

  public static int Write(Span < byte > slice, long value) {
    var val = (ulong) value;
    var written = 0;
    do {
      var temp = (byte)(val & 0b0111_1111);
      val >>= 7;
      if (val != 0) {
        temp |= 0b1000_0000;
      }

      slice[written++] = temp;
    } while (val != 0);

    return written;
  }
}