static float Integrate(const Curve &c, float x0, float x1) {
bool negate = false;
if (x0 > x1) {
std::swap(x0, x1);
negate = true;
}
int i0 = c.ToIndex(x0);
int i1 = c.ToIndex(x1 + c.dx);
i0 = std::min(std::max(i0, 0), c.size() - 1);
i1 = std::min(std::max(i1, 0), c.size() - 1);
float T = 0.5 * (c[i0] + c[i1]);
float M = 0;
for (int i = i0+2; i < i1; i += 2) {
T += c[i];
M += c[i-1];
}
float a = c.dx * (T + M);
return negate ? -a : a;
}
