First Byte   following   can encode values
               bytes        between
  xxxxxxx1       -       [ 0; 2^ 7-1 ]  // xxxx contains low bits of value
  xxxxxx10   [1  byte]   [ 0; 2^14-1 ]
  xxxxx100   [2 bytes]   [ 0; 2^21-1 ]
      .
      .
  x1000000   [6 bytes]   [ 0; 2^49-1 ]
  10000000   [7 bytes]   [ 0; 2^56-1 ]
  00000000   [8 bytes]   [ 0; 2^64-1 ]

int enc(unsigned char *result, unsigned long long int value) {
    int nUsedBits = 64 - __builtin_clzll(value|1);
    int nBytesNeeded = (nUsedBits+6)/7;
    if (nBytesNeeded<9) {
        value = ((value<<1)|1)<<(nBytesNeeded-1);
    } else {
        *result++ = 0;
    }
    __builtin_memcpy(result, &value, 8);
    return nBytesNeeded;
}