file_sys: Implement function to apply IPS patches

src/core/file_sys/ips_layer.cpp

+// Copyright 2018 yuzu emulator team
+// Licensed under GPLv2 or any later version
+// Refer to the license.txt file included.
+
+#include "common/assert.h"
+#include "common/swap.h"
+#include "core/file_sys/ips_layer.h"
+#include "core/file_sys/vfs_vector.h"
+
+namespace FileSys {
+
+enum class IPSFileType {
+    IPS,
+    IPS32,
+    Error,
+};
+
+static IPSFileType IdentifyMagic(const std::vector<u8>& magic) {
+    if (magic.size() != 5)
+        return IPSFileType::Error;
+    if (magic == std::vector<u8>{'P', 'A', 'T', 'C', 'H'})
+        return IPSFileType::IPS;
+    if (magic == std::vector<u8>{'I', 'P', 'S', '3', '2'})
+        return IPSFileType::IPS32;
+    return IPSFileType::Error;
+}
+
+VirtualFile PatchIPS(const VirtualFile& in, const VirtualFile& ips) {
+    if (in == nullptr || ips == nullptr)
+        return nullptr;
+
+    const auto type = IdentifyMagic(ips->ReadBytes(0x5));
+    if (type == IPSFileType::Error)
+        return nullptr;
+
+    auto in_data = in->ReadAllBytes();
+
+    std::vector<u8> temp(type == IPSFileType::IPS ? 3 : 4);
+    u64 offset = 5; // After header
+    while (ips->Read(temp.data(), temp.size(), offset) == temp.size()) {
+        offset += temp.size();
+        if (type == IPSFileType::IPS32 && temp == std::vector<u8>{'E', 'E', 'O', 'F'} ||
+            type == IPSFileType::IPS && temp == std::vector<u8>{'E', 'O', 'F'}) {
+            break;
+        }
+
+        u32 real_offset{};
+        if (type == IPSFileType::IPS32)
+            real_offset = (temp[0] << 24) | (temp[1] << 16) | (temp[2] << 8) | temp[3];
+        else
+            real_offset = (temp[0] << 16) | (temp[1] << 8) | temp[2];
+
+        u16 data_size{};
+        if (ips->ReadObject(&data_size, offset) != sizeof(u16))
+            return nullptr;
+        data_size = Common::swap16(data_size);
+        offset += sizeof(u16);
+
+        if (data_size == 0) { // RLE
+            u16 rle_size{};
+            if (ips->ReadObject(&rle_size, offset) != sizeof(u16))
+                return nullptr;
+            rle_size = Common::swap16(data_size);
+            offset += sizeof(u16);
+
+            const auto data = ips->ReadByte(offset++);
+            if (data == boost::none)
+                return nullptr;
+
+            if (real_offset + rle_size > in_data.size())
+                rle_size = in_data.size() - real_offset;
+            std::memset(in_data.data() + real_offset, data.get(), rle_size);
+        } else { // Standard Patch
+            auto read = data_size;
+            if (real_offset + read > in_data.size())
+                read = in_data.size() - real_offset;
+            if (ips->Read(in_data.data() + real_offset, read, offset) != data_size)
+                return nullptr;
+            offset += data_size;
+        }
+    }
+
+    if (temp != std::vector<u8>{'E', 'E', 'O', 'F'} && temp != std::vector<u8>{'E', 'O', 'F'})
+        return nullptr;
+    return std::make_shared<VectorVfsFile>(in_data, in->GetName(), in->GetContainingDirectory());
+}
+
+} // namespace FileSys

src/core/file_sys/ips_layer.h

+// Copyright 2018 yuzu emulator team
+// Licensed under GPLv2 or any later version
+// Refer to the license.txt file included.
+
+#pragma once
+
+#include <memory>
+
+#include "core/file_sys/vfs.h"
+
+namespace FileSys {
+
+VirtualFile PatchIPS(const VirtualFile& in, const VirtualFile& ips);
+
+} // namespace FileSys