Function cubicIntegrate

Engine/Interpolation.cpp:81–94

integrate from 0 to t

// integrate from 0 to t
static double
cubicIntegrate(double c0,
               double c1,
               double c2,
               double c3,
               double t)
{
    const double t2 = t * t;
    const double t3 = t2 * t;
    const double t4 = t3 * t;
    assert(t == t && t2 == t2 && t3 == t3 && t4 == t4 && c0 == c0 && c1 == c1 && c2 == c2 && c3 == c3);

    return (c0 ? c0 * t : 0.) + (c1 ? c1 * t2 / 2. : 0.) + (c2 ? c2 * t3 / 3 : 0.) + (c3 ? c3 * t4 / 4 : 0.);
}

// derive at t
static double