byteio - littleendianwriter_varint.go

  package byteio
  
  // WriteUintX writes the unsigned integer using a variable number of bytes
  // This variable encoding uses the first seven bits of each byte to encode
  // successive bits of the number, and the last bit to indicate that another
  // byte is to be read. The exception to this is the ninth byte, which uses its
  // highest bit to store the 64th bit of the number.
  // To allow for unique encodings of all numbers, as well as having a smaller
  // encoding for some numbers, the carry bit is also part of the number.
  // If there is another byte of the encoding then, by definition, the number
  // must be higher than what has currently been decoded. Thus, the next byte
  // starts at the next number.
  // For example, without this modification, the number 5 could be encoded as any
  // of the following: -
  // 0x05
  // 0x85, 0x00
  // 0x85, 0x80, 0x00
  // 0x85, 0x80, 0x80, 0x00
  // etc.
  //
  // By having the carry bit do double duty, adding 1 to the value of all bytes
  // where the carry bit is set, the only valid encoding of 5 becomes 0x05.
  func (e *LittleEndianWriter) WriteUintX(d uint64) (int, error) {
  	var pos int
  	for ; d > 127 && pos < 8; pos++ {
  		e.buffer[pos] = byte(d&0x7f) | 0x80
  		d >>= 7
  		d--
  	}
  	e.buffer[pos] = byte(d)
  	return e.Write(e.buffer[:pos+1])
  }
  
  // WriteIntX writes the integer using a variable number of bytes
  func (e *LittleEndianWriter) WriteIntX(d int64) (int, error) {
  	return e.WriteUintX(zigzag(d))
  }