From 7be66e9cb371bb5c656b20d08acd05e4b0e738df Mon Sep 17 00:00:00 2001
From: Christian Fehmer <fehmer@users.noreply.github.com>
Date: Mon, 24 Feb 2025 12:04:33 +0100
Subject: [PATCH] fix: rounding issues causing daily leaderboard to be out of
 order sometimes (@fehmer) (#6303)

---
 backend/__tests__/utils/misc.spec.ts | 14 ++++++++++++++
 backend/src/utils/misc.ts            |  6 ++++--
 2 files changed, 18 insertions(+), 2 deletions(-)

diff --git a/backend/__tests__/utils/misc.spec.ts b/backend/__tests__/utils/misc.spec.ts
index c4fb2c6ff..419a0876a 100644
--- a/backend/__tests__/utils/misc.spec.ts
+++ b/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 }) => {
diff --git a/backend/src/utils/misc.ts b/backend/src/utils/misc.ts
index d035c9cc6..9a66b4ef6 100644
--- a/backend/src/utils/misc.ts
+++ b/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;