REAL_UINT64 means real UINT64.
UINT64 means real UINT64 encoded with the following scheme:
Size of encoding sequence depends from first byte:
First_Byte Extra_Bytes Value
(binary)
0xxxxxxx : ( xxxxxxx )
10xxxxxx BYTE y[1] : ( xxxxxx << (8 * 1)) + y
110xxxxx BYTE y[2] : ( xxxxx << (8 * 2)) + y
...
1111110x BYTE y[6] : ( x << (8 * 6)) + y
11111110 BYTE y[7] : y
11111111 BYTE y[8] : y