qDebug() << "----Начало----";
double valueDouble1 = 5.53555454333;
double valueDouble2 = 1000.75645345533;

uint64_t value1 = *(uint64_t*)&valueDouble1;
uint64_t value2 = *(uint64_t*)&valueDouble2;;
uint64_t value3 = value2 ^ ((value2 ^ value1) & -(value2 < value1));

double valueDouble = *(double*)&value3;

qDebug() << "----Итог----";
qDebug() << valueDouble;