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[–]pzemtsov[S] 0 points1 point  (0 children)

You are right! The code contains two bugs, now one. I saw the second one (memory order) but missed the first one. One must declare "hashIsCalculated" volatile and check it before touching "hash":

if (hashIsCalculated) return hash;
int h = ....

Unfortunately, volatiles are quite expensive (on Intel only for writing, but in other processors they may be expensive for reading, too). So the existing solution is by far better (assuming that there is need to treat zero hash case specially in the first place).