Fix #349 emscripten alignment issue

emscripten/a.cpp

+#include <string>
+#include <fstream>
+#include <streambuf>
+#include <iostream>
+
+#define private public
+#include "rapidjson/document.h"
+
+int main() {
+    // std::ifstream in_file("config.json", std::ios::in);
+    rapidjson::Document json_config_;
+    // std::string json_string(
+    //         (std::istreambuf_iterator<char>(in_file)),
+    //         std::istreambuf_iterator<char>());
+    std::string json_string("{\"float_test\": 75.0}");
+    // if (!json_string.empty()) {
+        json_config_.Parse(json_string.c_str());
+    // }
+
+    printf("%p\n", &json_config_);
+    printf("%p\n", &json_config_.data_.o.members[0].value.data_.n.d);
+
+    std::cout << json_config_["float_test"].GetDouble() << std::endl;
+}
\ No newline at end of file

include/rapidjson/allocators.h

@@ -181,7 +181,7 @@ public:
         if (chunkHead_ == 0 || chunkHead_->size + size > chunkHead_->capacity)
             AddChunk(chunk_capacity_ > size ? chunk_capacity_ : size);
 
-        void *buffer = reinterpret_cast<char *>(chunkHead_ + 1) + chunkHead_->size;
+        void *buffer = reinterpret_cast<char *>(chunkHead_) + RAPIDJSON_ALIGN(sizeof(ChunkHeader)) + chunkHead_->size;
         chunkHead_->size += size;
         return buffer;
     }
@@ -199,7 +199,7 @@ public:
             return originalPtr;
 
         // Simply expand it if it is the last allocation and there is sufficient space
-        if (originalPtr == (char *)(chunkHead_ + 1) + chunkHead_->size - originalSize) {
+        if (originalPtr == (char *)(chunkHead_) + RAPIDJSON_ALIGN(sizeof(ChunkHeader)) + chunkHead_->size - originalSize) {
             size_t increment = static_cast<size_t>(newSize - originalSize);
             increment = RAPIDJSON_ALIGN(increment);
             if (chunkHead_->size + increment <= chunkHead_->capacity) {
@@ -231,7 +231,7 @@ private:
     void AddChunk(size_t capacity) {
         if (!baseAllocator_)
             ownBaseAllocator_ = baseAllocator_ = RAPIDJSON_NEW(BaseAllocator());
-        ChunkHeader* chunk = reinterpret_cast<ChunkHeader*>(baseAllocator_->Malloc(sizeof(ChunkHeader) + capacity));
+        ChunkHeader* chunk = reinterpret_cast<ChunkHeader*>(baseAllocator_->Malloc(RAPIDJSON_ALIGN(sizeof(ChunkHeader)) + capacity));
         chunk->capacity = capacity;
         chunk->size = 0;
         chunk->next = chunkHead_;

include/rapidjson/rapidjson.h

@@ -223,7 +223,7 @@
 
 //! Whether using 64-bit architecture
 #ifndef RAPIDJSON_64BIT
-#if defined(__LP64__) || defined(_WIN64)
+#if defined(__LP64__) || defined(_WIN64) || defined(__EMSCRIPTEN__)
 #define RAPIDJSON_64BIT 1
 #else
 #define RAPIDJSON_64BIT 0