From 5fc54809de3d4f1563428be0d3c50e756df68a27 Mon Sep 17 00:00:00 2001
From: Lee Stutzman <lstutzman@gmail.com>
Date: Fri, 3 Apr 2026 03:06:44 +0100
Subject: [PATCH] BUGFIX: Fix skillMaxUpgradeCount returning 1 at extreme skill
 levels (#2611)

---
 src/Bladeburner/Skill.ts            |  3 +++
 test/jest/Bladeburner/Skill.test.ts | 36 +++++++++++++++++++++++++++++
 2 files changed, 39 insertions(+)
 create mode 100644 test/jest/Bladeburner/Skill.test.ts

diff --git a/src/Bladeburner/Skill.ts b/src/Bladeburner/Skill.ts
index 3e6ed1e0a..70e704267 100644
--- a/src/Bladeburner/Skill.ts
+++ b/src/Bladeburner/Skill.ts
@@ -81,6 +81,9 @@ export class Skill {
   }
 
   calculateMaxUpgradeCount(currentLevel: number, cost: PositiveNumber): number {
+    // At extreme levels, floating-point precision loss makes currentLevel + 1 === currentLevel,
+    // causing calculateCost to return 0. No upgrade is possible in this case.
+    if (this.calculateCost(currentLevel, 1 as PositiveInteger) <= 0) return 0;
     /**
      * Define:
      * - x = count
diff --git a/test/jest/Bladeburner/Skill.test.ts b/test/jest/Bladeburner/Skill.test.ts
new file mode 100644
index 000000000..84b5a97eb
--- /dev/null
+++ b/test/jest/Bladeburner/Skill.test.ts
@@ -0,0 +1,36 @@
+import { BladeburnerMultName, BladeburnerSkillName } from "@enums";
+import { Skill } from "../../../src/Bladeburner/Skill";
+import { PositiveNumber } from "../../../src/types";
+
+const hyperdrive = new Skill({
+  name: BladeburnerSkillName.Hyperdrive,
+  desc: "test",
+  baseCost: 1,
+  costInc: 2.5,
+  mults: { [BladeburnerMultName.ExpGain]: 10 },
+});
+
+describe("Bladeburner Skill", () => {
+  describe("calculateMaxUpgradeCount", () => {
+    it("should return 0 when currentLevel is too high for floating-point precision", () => {
+      // At level 1e50, adding 1 is below float64 precision: 1e50 + 1 === 1e50
+      // So calculateCost returns 0 for any count, and no upgrade is possible
+      const result = hyperdrive.calculateMaxUpgradeCount(1e50, 1 as PositiveNumber);
+      expect(result).toBe(0);
+    });
+
+    it("should return correct count at normal levels", () => {
+      // At level 0 with cost 1, baseCost 1, costInc 2.5:
+      // cost of 1 level = round(1 * 1 * (1 + 2.5 * (0 + 0/2))) = round(1) = 1
+      const result = hyperdrive.calculateMaxUpgradeCount(0, 1 as PositiveNumber);
+      expect(result).toBe(1);
+    });
+
+    it("should return 0 when cost is less than the price of one level", () => {
+      // At level 10: cost of 1 level = round(1 * 1 * (1 + 2.5 * 10)) = 26
+      const costOfOne = hyperdrive.calculateCost(10);
+      const result = hyperdrive.calculateMaxUpgradeCount(10, (costOfOne - 1) as PositiveNumber);
+      expect(result).toBe(0);
+    });
+  });
+});