Every caller runs the collapse at p = 1, where power_mean still went the general way and spent a powf per value proving x^1 = x. At the mean it is one walk of the set with six accumulators live, two for a loss, and no scratch: the same addends in the same order, so the same floats. Change-Id: Ic98422d4a82f722a620e560b3346f748579c2f9f