From e5ae29b27ec4f6db17a21890a6bc4f4021232495 Mon Sep 17 00:00:00 2001
From: patchzyy <64382339+patchzyy@users.noreply.github.com>
Date: Mon, 24 Aug 2026 11:30:11 +0200
Subject: [PATCH] Create egg_decomp.cpp

---
 runtime/src/hle/egg_decomp.cpp | 61 ++++++++++++++++++++++++++++++++++
 1 file changed, 61 insertions(+)
 create mode 100644 runtime/src/hle/egg_decomp.cpp

diff --git a/runtime/src/hle/egg_decomp.cpp b/runtime/src/hle/egg_decomp.cpp
new file mode 100644
index 0000000..d1d2200
--- /dev/null
+++ b/runtime/src/hle/egg_decomp.cpp
@@ -0,0 +1,61 @@
+#include "hle_stubs.h"
+
+#include <cstdint>
+#include "memory.h"
+#include "runtime_log.h"
+
+// Native because a crafted Yaz0 run writes past the caller's buffer
+// (github.com/vabold/szsHaxx)
+// https://github.com/vabold/Kinoko/blob/main/source/egg/core/Decomp.cc
+
+extern "C" uint32_t EGG_Decomp_decodeSZS_80218c2c(uint32_t src, uint32_t dst)
+{
+    const uint32_t expandSize = (static_cast<uint32_t>(MemoryInline::FlatRead8(src + 4)) << 24) |
+                                (static_cast<uint32_t>(MemoryInline::FlatRead8(src + 5)) << 16) |
+                                (static_cast<uint32_t>(MemoryInline::FlatRead8(src + 6)) << 8) |
+                                static_cast<uint32_t>(MemoryInline::FlatRead8(src + 7));
+
+    uint32_t srcIdx = 16;
+    uint32_t dstIdx = 0;
+    uint32_t mask = 0;
+    uint32_t flags = 0;
+
+    while (static_cast<int32_t>(dstIdx) < static_cast<int32_t>(expandSize)) {
+        if (mask == 0) {
+            flags = MemoryInline::FlatRead8(src + srcIdx++);
+            mask = 0x80;
+        }
+
+        if ((flags & mask) != 0) {
+            MemoryInline::FlatWrite8(dst + dstIdx++, MemoryInline::FlatRead8(src + srcIdx++));
+        } else {
+            const uint32_t high = MemoryInline::FlatRead8(src + srcIdx);
+            const uint32_t low = MemoryInline::FlatRead8(src + srcIdx + 1);
+            srcIdx += 2;
+
+            const uint32_t rep = (high << 8) | low;
+            uint32_t copyIdx = dstIdx - (rep & 0xFFF) - 1;
+            uint32_t count = rep >> 12;
+            count = count != 0
+                        ? count + 2
+                        : static_cast<uint32_t>(MemoryInline::FlatRead8(src + srcIdx++)) + 18;
+
+            for (uint32_t i = 0; i < count; ++i) {
+                if (dstIdx >= expandSize) {
+                    RT_LOG(RT_TAG_HLE) << "decodeSZS: malformed stream from 0x" << std::hex << src
+                                       << std::dec << ", stopped after " << dstIdx << " of "
+                                       << expandSize << " bytes" << std::endl;
+                    return expandSize;
+                }
+                MemoryInline::FlatWrite8(dst + dstIdx++, MemoryInline::FlatRead8(dst + copyIdx++));
+            }
+        }
+
+        mask >>= 1;
+    }
+
+    return expandSize;
+}
+
+PPC_NATIVE_OVERRIDE(80218C2C, EGG_Decomp_decodeSZS_80218c2c, uint32_t,
+                    (uint32_t src, uint32_t dst), (src, dst));