From 8c8310f0bddc874a9f7f07c4158f0abc799357d4 Mon Sep 17 00:00:00 2001
From: Ali Mohammad Pur <ali.mpfard@gmail.com>
Date: Tue, 16 Jul 2024 14:02:21 +0200
Subject: [PATCH] LibWasm: Make Absolute/Negate<SignedIntegral> explicitly work
 mod 2^N

Previously we relied on signed overflow, this commit makes the same
behaviour explicit (avoiding UB in the process).
---
 .../LibWasm/AbstractMachine/Operators.h       | 26 +++++++++++++++++--
 1 file changed, 24 insertions(+), 2 deletions(-)

diff --git a/Userland/Libraries/LibWasm/AbstractMachine/Operators.h b/Userland/Libraries/LibWasm/AbstractMachine/Operators.h
index 5698b39386e..aa2d71ea5bf 100644
--- a/Userland/Libraries/LibWasm/AbstractMachine/Operators.h
+++ b/Userland/Libraries/LibWasm/AbstractMachine/Operators.h
@@ -505,14 +505,36 @@ struct PopCount {
 
 struct Absolute {
     template<typename Lhs>
-    auto operator()(Lhs lhs) const { return AK::abs(lhs); }
+    Lhs operator()(Lhs lhs) const
+    {
+        if constexpr (IsFloatingPoint<Lhs>)
+            return AK::abs(lhs);
+
+        if constexpr (IsSigned<Lhs>) {
+            if (lhs == NumericLimits<Lhs>::min())
+                return NumericLimits<Lhs>::min(); // Return the negation of _i_ modulo 2^N: https://www.w3.org/TR/wasm-core-2/#-hrefop-iabsmathrmiabs_n-i step 3
+        }
+
+        return AK::abs(lhs);
+    }
 
     static StringView name() { return "abs"sv; }
 };
 
 struct Negate {
     template<typename Lhs>
-    auto operator()(Lhs lhs) const { return -lhs; }
+    Lhs operator()(Lhs lhs) const
+    {
+        if constexpr (IsFloatingPoint<Lhs>)
+            return -lhs;
+
+        if constexpr (IsSigned<Lhs>) {
+            if (lhs == NumericLimits<Lhs>::min())
+                return NumericLimits<Lhs>::min(); // Return the negation of _i_ modulo 2^N: https://www.w3.org/TR/wasm-core-2/#-hrefop-iabsmathrmiabs_n-i step 3
+        }
+
+        return -lhs;
+    }
 
     static StringView name() { return "== 0"sv; }
 };