1 files changed, 192 insertions, 0 deletions
diff --git a/src/core/file_sys/vfs/vfs_concat.cpp b/src/core/file_sys/vfs/vfs_concat.cpp
new file mode 100644
index 000000000..b5cc9a9e9
--- /dev/null
+++ b/src/core/file_sys/vfs/vfs_concat.cpp
@@ -0,0 +1,192 @@
+// SPDX-FileCopyrightText: Copyright 2018 yuzu Emulator Project
+// SPDX-License-Identifier: GPL-2.0-or-later
+
+#include <algorithm>
+#include <utility>
+
+#include "common/assert.h"
+#include "core/file_sys/vfs/vfs_concat.h"
+#include "core/file_sys/vfs/vfs_static.h"
+
+namespace FileSys {
+
+ConcatenatedVfsFile::ConcatenatedVfsFile(std::string&& name_, ConcatenationMap&& concatenation_map_)
+    : concatenation_map(std::move(concatenation_map_)), name(std::move(name_)) {
+    DEBUG_ASSERT(this->VerifyContinuity());
+}
+
+bool ConcatenatedVfsFile::VerifyContinuity() const {
+    u64 last_offset = 0;
+    for (auto& entry : concatenation_map) {
+        if (entry.offset != last_offset) {
+            return false;
+        }
+
+        last_offset = entry.offset + entry.file->GetSize();
+    }
+
+    return true;
+}
+
+ConcatenatedVfsFile::~ConcatenatedVfsFile() = default;
+
+VirtualFile ConcatenatedVfsFile::MakeConcatenatedFile(std::string&& name,
+                                                      std::vector<VirtualFile>&& files) {
+    // Fold trivial cases.
+    if (files.empty()) {
+        return nullptr;
+    }
+    if (files.size() == 1) {
+        return files.front();
+    }
+
+    // Make the concatenation map from the input.
+    std::vector<ConcatenationEntry> concatenation_map;
+    concatenation_map.reserve(files.size());
+    u64 last_offset = 0;
+
+    for (auto& file : files) {
+        const auto size = file->GetSize();
+
+        concatenation_map.emplace_back(ConcatenationEntry{
+            .offset = last_offset,
+            .file = std::move(file),
+        });
+
+        last_offset += size;
+    }
+
+    return VirtualFile(new ConcatenatedVfsFile(std::move(name), std::move(concatenation_map)));
+}
+
+VirtualFile ConcatenatedVfsFile::MakeConcatenatedFile(
+    u8 filler_byte, std::string&& name, std::vector<std::pair<u64, VirtualFile>>&& files) {
+    // Fold trivial cases.
+    if (files.empty()) {
+        return nullptr;
+    }
+    if (files.size() == 1) {
+        return files.begin()->second;
+    }
+
+    // Make the concatenation map from the input.
+    std::vector<ConcatenationEntry> concatenation_map;
+
+    concatenation_map.reserve(files.size());
+    u64 last_offset = 0;
+
+    // Iteration of a multimap is ordered, so offset will be strictly non-decreasing.
+    for (auto& [offset, file] : files) {
+        const auto size = file->GetSize();
+
+        if (offset > last_offset) {
+            concatenation_map.emplace_back(ConcatenationEntry{
+                .offset = last_offset,
+                .file = std::make_shared<StaticVfsFile>(filler_byte, offset - last_offset),
+            });
+        }
+
+        concatenation_map.emplace_back(ConcatenationEntry{
+            .offset = offset,
+            .file = std::move(file),
+        });
+
+        last_offset = offset + size;
+    }
+
+    return VirtualFile(new ConcatenatedVfsFile(std::move(name), std::move(concatenation_map)));
+}
+
+std::string ConcatenatedVfsFile::GetName() const {
+    if (concatenation_map.empty()) {
+        return "";
+    }
+    if (!name.empty()) {
+        return name;
+    }
+    return concatenation_map.front().file->GetName();
+}
+
+std::size_t ConcatenatedVfsFile::GetSize() const {
+    if (concatenation_map.empty()) {
+        return 0;
+    }
+    return concatenation_map.back().offset + concatenation_map.back().file->GetSize();
+}
+
+bool ConcatenatedVfsFile::Resize(std::size_t new_size) {
+    return false;
+}
+
+VirtualDir ConcatenatedVfsFile::GetContainingDirectory() const {
+    if (concatenation_map.empty()) {
+        return nullptr;
+    }
+    return concatenation_map.front().file->GetContainingDirectory();
+}
+
+bool ConcatenatedVfsFile::IsWritable() const {
+    return false;
+}
+
+bool ConcatenatedVfsFile::IsReadable() const {
+    return true;
+}
+
+std::size_t ConcatenatedVfsFile::Read(u8* data, std::size_t length, std::size_t offset) const {
+    const ConcatenationEntry key{
+        .offset = offset,
+        .file = nullptr,
+    };
+
+    // Read nothing if the map is empty.
+    if (concatenation_map.empty()) {
+        return 0;
+    }
+
+    // Binary search to find the iterator to the first position we can check.
+    // It must exist, since we are not empty and are comparing unsigned integers.
+    auto it = std::prev(std::upper_bound(concatenation_map.begin(), concatenation_map.end(), key));
+    u64 cur_length = length;
+    u64 cur_offset = offset;
+
+    while (cur_length > 0 && it != concatenation_map.end()) {
+        // Check if we can read the file at this position.
+        const auto& file = it->file;
+        const u64 map_offset = it->offset;
+        const u64 file_size = file->GetSize();
+
+        if (cur_offset > map_offset + file_size) {
+            // Entirely out of bounds read.
+            break;
+        }
+
+        // Read the file at this position.
+        const u64 file_seek = cur_offset - map_offset;
+        const u64 intended_read_size = std::min<u64>(cur_length, file_size - file_seek);
+        const u64 actual_read_size =
+            file->Read(data + (cur_offset - offset), intended_read_size, file_seek);
+
+        // Update tracking.
+        cur_offset += actual_read_size;
+        cur_length -= actual_read_size;
+        it++;
+
+        // If we encountered a short read, we're done.
+        if (actual_read_size < intended_read_size) {
+            break;
+        }
+    }
+
+    return cur_offset - offset;
+}
+
+std::size_t ConcatenatedVfsFile::Write(const u8* data, std::size_t length, std::size_t offset) {
+    return 0;
+}
+
+bool ConcatenatedVfsFile::Rename(std::string_view new_name) {
+    return false;
+}
+
+} // namespace FileSys