From e9ad8d5e4f5a57faac5a627810034d3173d041f2 Mon Sep 17 00:00:00 2001
From: Andi Gallo <andigallo@proton.me>
Date: Fri, 4 Aug 2023 10:33:30 +0000
Subject: [PATCH] LibWeb: Use i64 for intermediate value in CSSPixels
 multiplication

Reduce the chance of overflow due to fixed point denominator being
squared when multiplying the raw values, before adjusting the final
value back.
---
 Tests/LibWeb/TestCSSPixels.cpp           | 8 ++++++++
 Userland/Libraries/LibWeb/PixelUnits.cpp | 2 +-
 2 files changed, 9 insertions(+), 1 deletion(-)

diff --git a/Tests/LibWeb/TestCSSPixels.cpp b/Tests/LibWeb/TestCSSPixels.cpp
index 7c78cbab9d..99c839a7ba 100644
--- a/Tests/LibWeb/TestCSSPixels.cpp
+++ b/Tests/LibWeb/TestCSSPixels.cpp
@@ -87,4 +87,12 @@ TEST_CASE(saturated_subtraction)
     EXPECT_EQ(value - -1, CSSPixels(INFINITY));
 }
 
+TEST_CASE(multiplication_uses_i64_for_raw_values)
+{
+    CSSPixels a(1200);
+    CSSPixels b(647);
+    CSSPixels c = a * b;
+    EXPECT_EQ(c, CSSPixels(776400));
+}
+
 }
diff --git a/Userland/Libraries/LibWeb/PixelUnits.cpp b/Userland/Libraries/LibWeb/PixelUnits.cpp
index 6fc367a8f3..e8077bb630 100644
--- a/Userland/Libraries/LibWeb/PixelUnits.cpp
+++ b/Userland/Libraries/LibWeb/PixelUnits.cpp
@@ -119,7 +119,7 @@ CSSPixels CSSPixels::operator-(CSSPixels const& other) const
 CSSPixels CSSPixels::operator*(CSSPixels const& other) const
 {
     CSSPixels result;
-    result.set_raw_value((raw_value() * other.raw_value()) >> fractional_bits);
+    result.set_raw_value((static_cast<i64>(raw_value()) * other.raw_value()) >> fractional_bits);
     return result;
 }