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WIP/fs/fssystem/fssystem_pooled_buffer.cpp

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+// SPDX-FileCopyrightText: Copyright 2023 yuzu Emulator Project
+// SPDX-License-Identifier: GPL-2.0-or-later
+
+#include "common/alignment.h"
+#include "core/file_sys/fssystem/fssystem_pooled_buffer.h"
+
+namespace FileSys {
+
+namespace {
+
+constexpr size_t HeapBlockSize = BufferPoolAlignment;
+static_assert(HeapBlockSize == 4_KiB);
+
+// A heap block is 4KiB. An order is a power of two.
+// This gives blocks of the order 32KiB, 512KiB, 4MiB.
+constexpr s32 HeapOrderMax = 7;
+constexpr s32 HeapOrderMaxForLarge = HeapOrderMax + 3;
+
+constexpr size_t HeapAllocatableSizeMax = HeapBlockSize * (static_cast<size_t>(1) << HeapOrderMax);
+constexpr size_t HeapAllocatableSizeMaxForLarge =
+    HeapBlockSize * (static_cast<size_t>(1) << HeapOrderMaxForLarge);
+
+} // namespace
+
+size_t PooledBuffer::GetAllocatableSizeMaxCore(bool large) {
+    return large ? HeapAllocatableSizeMaxForLarge : HeapAllocatableSizeMax;
+}
+
+void PooledBuffer::AllocateCore(size_t ideal_size, size_t required_size, bool large) {
+    // Ensure preconditions.
+    ASSERT(m_buffer == nullptr);
+
+    // Check that we can allocate this size.
+    ASSERT(required_size <= GetAllocatableSizeMaxCore(large));
+
+    const size_t target_size =
+        std::min(std::max(ideal_size, required_size), GetAllocatableSizeMaxCore(large));
+
+    // Dummy implementation for allocate.
+    if (target_size > 0) {
+        m_buffer =
+            reinterpret_cast<char*>(::operator new(target_size, std::align_val_t{HeapBlockSize}));
+        m_size = target_size;
+
+        // Ensure postconditions.
+        ASSERT(m_buffer != nullptr);
+    }
+}
+
+void PooledBuffer::Shrink(size_t ideal_size) {
+    ASSERT(ideal_size <= GetAllocatableSizeMaxCore(true));
+
+    // Shrinking to zero means that we have no buffer.
+    if (ideal_size == 0) {
+        ::operator delete(m_buffer, std::align_val_t{HeapBlockSize});
+        m_buffer = nullptr;
+        m_size = ideal_size;
+    }
+}
+
+} // namespace FileSys