Merge pull request #9453 from ameerj/scratch-vector

common: Add ScratchBuffer Class

3 files changed, 122 insertions, 0 deletions

diff --git a/src/common/CMakeLists.txt b/src/common/CMakeLists.txt
index 25b22a281..eb05e46a8 100644
--- a/src/common/CMakeLists.txt
+++ b/src/common/CMakeLists.txt
@@ -78,6 +78,7 @@ add_library(common STATIC
     logging/types.h
     lz4_compression.cpp
     lz4_compression.h
+    make_unique_for_overwrite.h
     math_util.h
     memory_detect.cpp
     memory_detect.h
@@ -101,6 +102,7 @@ add_library(common STATIC
     ${CMAKE_CURRENT_BINARY_DIR}/scm_rev.cpp
     scm_rev.h
     scope_exit.h
+    scratch_buffer.h
     settings.cpp
     settings.h
     settings_input.cpp
diff --git a/src/common/make_unique_for_overwrite.h b/src/common/make_unique_for_overwrite.h
new file mode 100644
index 000000000..c7413cf51
--- /dev/null
+++ b/src/common/make_unique_for_overwrite.h
@@ -0,0 +1,25 @@
+// SPDX-FileCopyrightText: Copyright 2022 yuzu Emulator Project
+// SPDX-License-Identifier: GPL-2.0-or-later
+
+#pragma once
+
+#include <memory>
+#include <type_traits>
+
+namespace Common {
+
+template <class T>
+requires(!std::is_array_v<T>) std::unique_ptr<T> make_unique_for_overwrite() {
+    return std::unique_ptr<T>(new T);
+}
+
+template <class T>
+requires std::is_unbounded_array_v<T> std::unique_ptr<T> make_unique_for_overwrite(std::size_t n) {
+    return std::unique_ptr<T>(new std::remove_extent_t<T>[n]);
+}
+
+template <class T, class... Args>
+requires std::is_bounded_array_v<T>
+void make_unique_for_overwrite(Args&&...) = delete;
+
+} // namespace Common
diff --git a/src/common/scratch_buffer.h b/src/common/scratch_buffer.h
new file mode 100644
index 000000000..1245a5086
--- /dev/null
+++ b/src/common/scratch_buffer.h
@@ -0,0 +1,95 @@
+// SPDX-FileCopyrightText: Copyright 2022 yuzu Emulator Project
+// SPDX-License-Identifier: GPL-2.0-or-later
+
+#pragma once
+
+#include "common/make_unique_for_overwrite.h"
+
+namespace Common {
+
+/**
+ * ScratchBuffer class
+ * This class creates a default initialized heap allocated buffer for cases such as intermediate
+ * buffers being copied into entirely, where value initializing members during allocation or resize
+ * is redundant.
+ */
+template <typename T>
+class ScratchBuffer {
+public:
+    ScratchBuffer() = default;
+
+    explicit ScratchBuffer(size_t initial_capacity)
+        : last_requested_size{initial_capacity}, buffer_capacity{initial_capacity},
+          buffer{Common::make_unique_for_overwrite<T[]>(initial_capacity)} {}
+
+    ~ScratchBuffer() = default;
+
+    /// This will only grow the buffer's capacity if size is greater than the current capacity.
+    /// The previously held data will remain intact.
+    void resize(size_t size) {
+        if (size > buffer_capacity) {
+            auto new_buffer = Common::make_unique_for_overwrite<T[]>(size);
+            std::move(buffer.get(), buffer.get() + buffer_capacity, new_buffer.get());
+            buffer = std::move(new_buffer);
+            buffer_capacity = size;
+        }
+        last_requested_size = size;
+    }
+
+    /// This will only grow the buffer's capacity if size is greater than the current capacity.
+    /// The previously held data will be destroyed if a reallocation occurs.
+    void resize_destructive(size_t size) {
+        if (size > buffer_capacity) {
+            buffer_capacity = size;
+            buffer = Common::make_unique_for_overwrite<T[]>(buffer_capacity);
+        }
+        last_requested_size = size;
+    }
+
+    [[nodiscard]] T* data() noexcept {
+        return buffer.get();
+    }
+
+    [[nodiscard]] const T* data() const noexcept {
+        return buffer.get();
+    }
+
+    [[nodiscard]] T* begin() noexcept {
+        return data();
+    }
+
+    [[nodiscard]] const T* begin() const noexcept {
+        return data();
+    }
+
+    [[nodiscard]] T* end() noexcept {
+        return data() + last_requested_size;
+    }
+
+    [[nodiscard]] const T* end() const noexcept {
+        return data() + last_requested_size;
+    }
+
+    [[nodiscard]] T& operator[](size_t i) {
+        return buffer[i];
+    }
+
+    [[nodiscard]] const T& operator[](size_t i) const {
+        return buffer[i];
+    }
+
+    [[nodiscard]] size_t size() const noexcept {
+        return last_requested_size;
+    }
+
+    [[nodiscard]] size_t capacity() const noexcept {
+        return buffer_capacity;
+    }
+
+private:
+    size_t last_requested_size{};
+    size_t buffer_capacity{};
+    std::unique_ptr<T[]> buffer{};
+};
+
+} // namespace Common