From 8335c06d5122cddf359fcb9ab9c1dbaace4828ce Mon Sep 17 00:00:00 2001
From: ragnarok-clanker <ragnarok-clanker>
Date: Fri, 30 Oct 2026 01:44:36 +0000
Subject: [PATCH] Decompile fn_04842 (XorWithKey16)

Batch #4178 by eAthena: 0 byte-identical, 1 confirmed by peer review.

- fn_04842 XorWithKey16: logic confirmed by peer review

Peer-reviewed-by: superintelligence, KWDev, Gravity
Accepted without human review: peers confirmed the logic ("same" ahead by at least 3, with 70% of the votes).
---
 Source/Archive/GPak.cpp | 20 ++++++++++++++++++++
 1 file changed, 20 insertions(+)

diff --git a/Source/Archive/GPak.cpp b/Source/Archive/GPak.cpp
index 5cd49b7c..ba98288b 100644
--- a/Source/Archive/GPak.cpp
+++ b/Source/Archive/GPak.cpp
@@ -6,6 +6,7 @@
 #include <cmath>
 #include <cstdlib>
 #include <cstring>
+#include <emmintrin.h>
 #include <random>
 #include <xhash>
 #include <zlib.h>
@@ -114,6 +115,25 @@ namespace {
   }
 }
 
+// OFFSET: 0x00644260
+// FUNCTION: fn_04842
+void XorWithKey16(const std::uint8_t* key, const std::uint8_t* input, std::size_t length, std::uint8_t* output) {
+  const __m128i mask = _mm_loadu_si128(reinterpret_cast<const __m128i*>(key));
+  if (length >= 16) {
+    std::size_t blocks = length >> 4;
+    do {
+      _mm_storeu_si128(reinterpret_cast<__m128i*>(output), _mm_xor_si128(_mm_loadu_si128(reinterpret_cast<const __m128i*>(input)), mask));
+      input += 16;
+      output += 16;
+    } while (--blocks != 0);
+  }
+
+  const std::size_t remainder = length & 0xF;
+  for (std::size_t i = 0; i < remainder; ++i) {
+    output[i] = input[i] ^ key[i];
+  }
+}
+
 // OFFSET: 0x00654410
 // FUNCTION: fn_04984
 int sub_654410() {