A hundred billion operations is spinning on a loop for a couple minutes, so not really.
It took about ten minutes at full system utilization on all cores, running the "torture test" in a loop in each thread.
For a cosmic ray bit-flip, or to perform a hundred billion operations?
One hundred billion operations. The machine didn't have ECC memory, so a bit flip is a possible explanation. I should have checked if it was reproducible with ECC.
I still think a logic bug or compiler bug was at fault though.