skiplistNodeHeightSelection.cpp

static inline uint8_t RHeight(void)
{
        // Assuming probability 1/2 of an element appearing in layer i also appearing in layer i + 1
        // We can do the usual toss-the-coin dance, or we can just use RNG once and count the trailing zeros.
        // Instead of using a loop to count, we can isolate the rightmost 0-bit, turn off all bits and sets that bit to 1, and then
        // just compute count of trailing zeros instead.
        const auto r = rand();
        const auto v = ~r & (r + 1);
        const uint8_t tz = __builtin_ctz(v);

        // We can't return 0, and we don't want to use a branch here, so we have to be creative
        return 1 ^ ((1 ^ tz) & -(1 < tz));
}