Persistent state between frames

I have a layer with a car, and I have another Null layer with a speed controller that has manually placed keyframes.

I want to control the car position according to those speed keyframes, i.e. accumulate traveled distance. For example, if the spped values on the first 5 frames are 1, 2, 3, 4, 5 then positions should be 1, 3, 6, 10, 15.

I wrote this script and it works as intended:

sourceLayer = thisComp.layer("Null 1");
currentFrame = timeToFrames();

sum = 0;
for(i = 0; i <= currentFrame; i++) {
sum += sourceLayer.effect("speed")("Slider").valueAtTime(framesToTime(i));
}
sum

This becomes very inefficient as currentFrame increases. In reality I need some kind of persistent across frames storage, so I could just add one value to it every frame. Is that possible to do in Ae scripting system?