::random (from -1.0 to 1.0)

#include <cmath>
#include <cstdlib>
#include <limits>

double random() {

    constexpr double EPSILON = std::numeric_limits<double>::epsilon();

    const double RANDOM = std::rand();

    const double STAGE_1 = ((2.0 * RANDOM) / RAND_MAX) - 1.0;
    const double STAGE_2 = STAGE_1 - std::copysign(EPSILON, STAGE_1);

    return STAGE_2;

}