fix: rounding issues causing daily leaderboard to be out of order sometimes (@fehmer) (monkeytypegame#6303)

Author: fehmer

backend/__tests__/utils/misc.spec.ts

@@ -62,6 +62,20 @@ describe("Misc Utils", () => {
         timestamp: 1653591901000,
         expectedScore: 1196200960717699,
       },
+      {
+        wpm: 196.205,
+        acc: 96.075,
+        timestamp: 1653591901000,
+        expectedScore: 1196210960817699,
+      },
+      {
+        // this one is particularly important - in JS 154.39 * 100 is equal to 15438.999999999998
+        // thanks floating point errors!
+        wpm: 154.39,
+        acc: 96.14,
+        timestamp: 1740333827000,
+        expectedScore: 1154390961421373,
+      },
     ];
 
     _.each(testCases, ({ wpm, acc, timestamp, expectedScore }) => {

backend/src/utils/misc.ts

@@ -67,8 +67,10 @@ export function matchesAPattern(text: string, pattern: string): boolean {
 }
 
 export function kogascore(wpm: number, acc: number, timestamp: number): number {
-  const normalizedWpm = Math.floor(wpm * 100);
-  const normalizedAcc = Math.floor(acc * 100);
+  // its safe to round after multiplying by 100 (99.99 * 100 rounded will be 9999 not 100)
+  // rounding is necessary to protect against floating point errors
+  const normalizedWpm = Math.round(wpm * 100);
+  const normalizedAcc = Math.round(acc * 100);
 
   const padAmount = 100000;
   const firstPart = (padAmount + normalizedWpm) * padAmount;