How to implement talib's LINEARREG_SLOPE function with js?

Question

The TaLib's code: https://sourceforge.net/p/ta-lib/code/HEAD/tree/trunk/ta-lib/c/src/ta_func/ta_LINEARREG_SLOPE.c#l331

I want a JavaScript function like this:

functuin linearRegressionSlope(arr, range) {
  return [...slopeVal]
}

I tried to implement one according to the above source code, but found that the result is inconsistent with it:

const data = [1,2,3,4,5,6,7,8,9,10,11,12,13,14,15,16,17,18,19,20]
let today = 0
const optInTimePeriod = 5
const SumX = optInTimePeriod * (optInTimePeriod - 1) * 0.5
const SumXSqr =
  (optInTimePeriod * (optInTimePeriod - 1) * (2 * optInTimePeriod - 1)) / 6
const Divisor = SumX * SumX - optInTimePeriod * SumXSqr
const outReal = []
while (today <= data.length - 1) {
  let SumXY = 0
  let SumY = 0
  for (let i = optInTimePeriod; i > 0; i--) {
    SumY += data[today - i]
    SumXY += i * data[today - i]
  }
  outReal.push((optInTimePeriod * SumXY - SumX * SumY) / Divisor)
  today++
}
console.log(outReal)

And you can test it by talib-binding

const {LINEARREG_SLOPE} = require('talib-binding')
console.log(LINEARREG_SLOPE(data, optInTimePeriod))

Answer 1

The original code has for loop is like

    for(int i = 5; i-- != 0; )
      printf("%d ", i);

which prints out: 4 3 2 1 0

and your loop iterates 5 4 3 2 1. perhaps it's the reason.