Function _memory_allocate_from_heap

vm/ByteCodeTranslator/src/rpmalloc.c:611–748

Allocate a small/medium sized memory block from the given heap

//! Allocate a small/medium sized memory block from the given heap
static void*
_memory_allocate_from_heap(heap_t* heap, size_t size) {
#if ENABLE_STATISTICS
	//For statistics we need to store the requested size in the memory block
	size += sizeof(size_t);
#endif

	//Calculate the size class index and do a dependent lookup of the final class index (in case of merged classes)
	const size_t class_idx = _memory_size_class[(size <= SMALL_SIZE_LIMIT) ?
		((size + (SMALL_GRANULARITY - 1)) >> SMALL_GRANULARITY_SHIFT) - 1 :
		SMALL_CLASS_COUNT + ((size - SMALL_SIZE_LIMIT + (MEDIUM_GRANULARITY - 1)) >> MEDIUM_GRANULARITY_SHIFT) - 1].class_idx;

	span_block_t* active_block = heap->active_block + class_idx;
	size_class_t* size_class = _memory_size_class + class_idx;
	const count_t class_size = size_class->size;

#if ENABLE_STATISTICS
	heap->allocated += class_size;
	heap->requested += size;
#endif

	//Step 1: Try to get a block from the currently active span. The span block bookkeeping
	//        data for the active span is stored in the heap for faster access
use_active:
	if (active_block->free_count) {
		//Happy path, we have a span with at least one free block
		span_t* span = heap->active_span[class_idx];
		count_t offset = class_size * active_block->free_list;
		uint32_t* block = pointer_offset(span, SPAN_HEADER_SIZE + offset);
		assert(span);

		--active_block->free_count;
		if (!active_block->free_count) {
			//Span is now completely allocated, set the bookkeeping data in the
			//span itself and reset the active span pointer in the heap
			span->data.block.free_count = 0;
			span->data.block.first_autolink = (uint16_t)size_class->block_count;
			heap->active_span[class_idx] = 0;
		}
		else {
			//Get the next free block, either from linked list or from auto link
			if (active_block->free_list < active_block->first_autolink) {
				active_block->free_list = (uint16_t)(*block);
			}
			else {
				++active_block->free_list;
				++active_block->first_autolink;
			}
			assert(active_block->free_list < size_class->block_count);
		}

#if ENABLE_STATISTICS
		//Store the requested size for statistics
		*(size_t*)pointer_offset(block, class_size - sizeof(size_t)) = size;
#endif

		return block;
	}