DOCUMENTATION: Clarify getSkillUpgradeCost and fix typo in BaseTask (b…

…itburner-official#1749)

markdown/bitburner.bladeburner.getskillupgradecost.md

@@ -31,5 +31,11 @@ RAM cost: 4 GB
 
 This function returns the number of skill points needed to upgrade the specified skill the specified number of times.
 
-The function returns Infinity if the sum of the current level and count exceeds the maximum level.
+The function may return 0 or Infinity in special cases:
+
+- Return 0 if the current skill level is too high and the specified count is too small. In normal situations, you don't need to worry about this case. It only happens when involved numbers surpass Number.MAX\_SAFE\_INTEGER and be affected by the floating-point inaccuracy.
+
+- Return Infinity if the sum of the current level and count exceeds the maximum level.
+
+[skillMaxUpgradeCount](./bitburner.bladeburnerformulas.skillmaxupgradecount.md) is the inverse function of this one.
 

src/ScriptEditor/NetscriptDefinitions.d.ts

@@ -1653,7 +1653,7 @@ export interface TIX {
  */
 export interface BaseTask {
   /**
-   * The number of game engine cycles that has passed since this task started. 1 engine cycle = 200ms.
+   * The number of game engine cycles has passed since this task started. 1 engine cycle = 200ms.
    */
   cyclesWorked: number;
 }
@@ -3584,7 +3584,15 @@ export interface Bladeburner {
    *
    * This function returns the number of skill points needed to upgrade the specified skill the specified number of times.
    *
-   * The function returns Infinity if the sum of the current level and count exceeds the maximum level.
+   * The function may return 0 or Infinity in special cases:
+   *
+   * - Return 0 if the current skill level is too high and the specified count is too small. In normal situations, you
+   * don't need to worry about this case. It only happens when involved numbers surpass Number.MAX_SAFE_INTEGER and be
+   * affected by the floating-point inaccuracy.
+   *
+   * - Return Infinity if the sum of the current level and count exceeds the maximum level.
+   *
+   * {@link BladeburnerFormulas.skillMaxUpgradeCount | skillMaxUpgradeCount} is the inverse function of this one.
    *
    * @param skillName - Name of skill. Case-sensitive and must be an exact match.
    * @param count - Number of times to upgrade the skill. Defaults to 1 if not specified.