significand
uint64_t significand;
while (__predict_false((significand = random64()) == 0)) {
shift = clz64(significand);
significand <<= shift;
significand |= (random64() >> (64 - shift));
significand |= 1;
return ldexp((double)significand, exponent);
double significand(double);
PROTO_DEPRECATED(significand);