Function get_block_index_index_for_index

deps/concurrentqueue/concurrentqueue.h:2931–2947

		}
		
		inline size_t get_block_index_index_for_index(index_t index, BlockIndexHeader*& localBlockIndex) const
		{
#ifdef MCDBGQ_NOLOCKFREE_IMPLICITPRODBLOCKINDEX
			debug::DebugLock lock(mutex);
#endif
			index &= ~static_cast<index_t>(BLOCK_SIZE - 1);
			localBlockIndex = blockIndex.load(std::memory_order_acquire);
			auto tail = localBlockIndex->tail.load(std::memory_order_acquire);
			auto tailBase = localBlockIndex->index[tail]->key.load(std::memory_order_relaxed);
			assert(tailBase != INVALID_BLOCK_BASE);
			// Note: Must use division instead of shift because the index may wrap around, causing a negative
			// offset, whose negativity we want to preserve
			auto offset = static_cast<size_t>(static_cast<typename std::make_signed<index_t>::type>(index - tailBase) / BLOCK_SIZE);
			size_t idx = (tail + offset) & (localBlockIndex->capacity - 1);
			assert(localBlockIndex->index[idx]->key.load(std::memory_order_relaxed) == index && localBlockIndex->index[idx]->value.load(std::memory_order_relaxed) != nullptr);
			return idx;
		}
		
		bool new_block_index()
		{