RapidJSON: add aligned memory allocator class

Added, but not implemented yet. We can revisit this in the future and check if its worth using the aligned memory allocator.

src/core/stdafx.h

@@ -32,6 +32,17 @@
 namespace rapidjson { typedef ::std::size_t SizeType; }
 
 #include "rapidjson/rapidjson.h"
+
+#ifdef RAPIDJSON_USE_CUSTOM_ALLOCATOR
+// Must be included before the RapidJSON includes
+// as this replaces the default allocator. The new
+// allocator takes SIMD alignment into account, but
+// isn't strictly necessary when using RAPIDJSON_SIMD.
+#include "tier2/jsonalloc.h"
+#define RAPIDJSON_DEFAULT_ALLOCATOR ::RAPIDJSON_NAMESPACE::MemoryPoolAllocator<JSONAllocator>
+#define RAPIDJSON_DEFAULT_STACK_ALLOCATOR ::RAPIDJSON_NAMESPACE::MemoryPoolAllocator<JSONAllocator>
+#endif // RAPIDJSON_USE_CUSTOM_ALLOCATOR
+
 #include "rapidjson/document.h"
 #include "rapidjson/writer.h"
 #include "rapidjson/stringbuffer.h"

src/public/tier2/jsonalloc.h

@@ -0,0 +1,74 @@
+//===========================================================================//
+//
+// Purpose: RapidJSON allocator class
+//
+//===========================================================================//
+#ifndef TIER2_JSONALLOC_H
+#define TIER2_JSONALLOC_H
+
+// 16 byte alignment as we only support up to 128 bits SIMD.
+#define JSON_SIMD_ALIGNMENT 16
+
+class JSONAllocator
+{
+public:
+    static const bool kNeedFree;    //!< Whether this allocator needs to call Free().
+
+    // Allocate a memory block.
+    // \param size of the memory block in bytes.
+    // \returns pointer to the memory block.
+    void* Malloc(size_t size)
+    {
+        if (!size)
+            return nullptr;
+
+#ifdef RAPIDJSON_SIMD
+        return _aligned_malloc(AlignValue(size, JSON_SIMD_ALIGNMENT), JSON_SIMD_ALIGNMENT);
+#else
+        return malloc(size);
+#endif
+    }
+
+    // Resize a memory block.
+    // \param originalPtr The pointer to current memory block. Null pointer is permitted.
+    // \param originalSize The current size in bytes. (Design issue: since some allocator may not book-keep this, explicitly pass to it can save memory.)
+    // \param newSize the new size in bytes.
+    void* Realloc(void* originalPtr, size_t originalSize, size_t newSize)
+    {
+        (void)originalSize;
+
+        if (newSize == 0)
+        {
+            Free(originalPtr);
+            return nullptr;
+        }
+
+#ifdef RAPIDJSON_SIMD
+        return _aligned_realloc(originalPtr, AlignValue(newSize, JSON_SIMD_ALIGNMENT), JSON_SIMD_ALIGNMENT);
+#else
+        return realloc(originalPtr, newSize);
+#endif
+    }
+
+    // Free a memory block.
+    // \param pointer to the memory block. Null pointer is permitted.
+    static void Free(void* ptr) noexcept
+    {
+#ifdef RAPIDJSON_SIMD
+        _aligned_free(ptr);
+#else
+        free(ptr);
+#endif
+    }
+
+    bool operator==(const JSONAllocator&) const noexcept
+    {
+        return true;
+    }
+    bool operator!=(const JSONAllocator&) const noexcept
+    {
+        return false;
+    }
+};
+
+#endif // TIER2_JSONALLOC_H