mempool: Document unsigned integer wraparounds in CTxMemPoolEntry::UpdateAncestorState(...) #14218

 313 | @@ -314,11 +314,16 @@ void CTxMemPoolEntry::UpdateDescendantState(int64_t modifySize, CAmount modifyFe
 314 |  
 315 |  void CTxMemPoolEntry::UpdateAncestorState(int64_t modifySize, CAmount modifyFee, int64_t modifyCount, int64_t modifySigOps)
 316 |  {
 317 | +    // An unsigned integer wraparound may take place here (modifySize is allowed to be negative).
 318 |      nSizeWithAncestors += modifySize;
 319 |      assert(int64_t(nSizeWithAncestors) > 0);

MarcoFalke commented at 12:56 PM on September 14, 2018:

I don't think this can wrap around in normal operation, since it is always first increased by some modifySize and only later reduced by the same modifySize.

Also, note the assert, which would be hit if a wraparound occurs.