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58666ed28a
The first iteration of the signal-checking loop would compute sigmask(0) which expands to 1<<(-1) which is undefined behavior according to the C standard. The lack of field reports of trouble suggest that it evaluates to 0 on all existing Windows compilers, but that's hardly something to rely on. Since signal 0 isn't a queueable signal anyway, we can just make the loop iterate from 1 instead, and save a few cycles as well as avoiding the undefined behavior. In passing, avoid evaluating the volatile expression UNBLOCKED_SIGNAL_QUEUE twice in a row; there's no reason to waste cycles like that. Noted by Aleksander Alekseev, though this isn't his proposed fix. Back-patch to all supported branches.