API: skillMaxUpgradeCount returns 1 when SP is too small and current level is too high

[catloversg]

#1475 added skillMaxUpgradeCount formula API.

When the skill point (SP) is not enough to upgrade the skill, this API should return 0. However, due to floating-point imprecision, when SP is too small and the current level is too high, this API may return 1. For example:

ns.print(ns.formulas.bladeburner.skillMaxUpgradeCount("Hyperdrive", 1e50, 1)); // Print 1

This is how we are implementing it:

const result = Math.round((m + delta) / this.costInc);
const costOfResultPlus1 = this.calculateCost(currentLevel, (result + 1) as PositiveInteger);
if (costOfResultPlus1 <= cost) {
  return result + 1;
}
const costOfResult = this.calculateCost(currentLevel, result as PositiveInteger);
if (costOfResult <= cost) {
  return result;
}
return result - 1;

result is 0, cost is 1, and costOfResultPlus1 is 0, so it returns 1. In this case, the current level is too high (1e50), so increasing it by 1 (result + 1) won't do anything (costOfResultPlus1 = 0) (if the player calls ns.bladeburner.upgradeSkill with count = 1, we will notify them that it's impossible to do that).

At first glance, I think that this behavior is (somewhat ?) reasonable. However, some players may be confused: "Why does it return 1 when it's obvious that I won't be able to upgrade the skill with that amount of SP?".

@d0sboots What do you think about this problem? It only matters when the player is farming int and they don't know the pitfall of floating-point imprecision (A(big) + B(small) may be exactly A in some cases), so I don't think that it's a big deal.

[d0sboots]

I think there's an actual problem here. For the right large values, I think the "result" calculation in skillMaxUpgradeCount can return a single number that is some power-of-2 due to rounding in the fundamental calculation. However, this result will be too big, and then the +-1 won't be enough to correct that, so the final result ends up being too big and fails if you try to pass it through on the other side.

Instead of using +-1, it needs to be using increments that are it minimum 1, but scale with the precision of the calculation. Ugh.

[Alpheus]

Isn't max level on all skills 1e18?
Nevermind, this is dev, I was looking at 2.6.2.

I'm adding draft PR to test cover the bugged behavior with some additional cases.