klish/lub/heap/heap_slice_from_bottom.c

#include <assert.h>

#include "private.h"
/*--------------------------------------------------------- */
void *lub_heap_slice_from_bottom(lub_heap_t * this,
				 lub_heap_free_block_t ** ptr_block,
				 words_t * words, bool_t seg_start)
{
	void *result = NULL;
	lub_heap_free_block_t *block = *ptr_block;

	/* check this is a free block */
	assert(1 == block->tag.free);

	if (BOOL_TRUE == lub_heap_block_check((lub_heap_block_t *) block)
	    && (*words <= block->tag.words)) {
		words_t new_words = (block->tag.words - *words);

		/* get the tag at the end of the current free block */
		lub_heap_tag_t *tail =
		    lub_heap_block__get_tail((lub_heap_block_t *) block);

		/* 
		 * Is there sufficient memory to perform the task? 
		 * we must leave enough space for the free block to work
		 */
		if (new_words > (sizeof(lub_heap_free_block_t) >> 2)) {
			lub_heap_free_block_t *new_block;

			/* adjust the free block size */
			tail->words -= *words;

			/* create a new free block header */
			new_block =
			    (lub_heap_free_block_t *) (&block->tag + *words);
			new_block->tag.segment = seg_start;
			new_block->tag.free = 1;	/* this is a free block */
			new_block->tag.words = tail->words;

			/* update the stats */
			this->stats.free_bytes -= (*words << 2);

			/* set up the tree node */
			lub_bintree_node_init(&new_block->bt_node);

			result = block;
			*ptr_block = new_block;
		} else {
			/* 
			 * there is only just enough space for the request
			 * so we also throw in the memory used for the tags
			 */
			--this->stats.free_blocks;
			this->stats.free_bytes -= (block->tag.words << 2);
			this->stats.free_bytes +=
			    sizeof(lub_heap_alloc_block_t);
			this->stats.free_overhead -=
			    sizeof(lub_heap_alloc_block_t);
			/* update the client's word count */
			*words = block->tag.words;

			/* there is no free block left!!! */
			result = block;
			*ptr_block = NULL;
		}
		if (NULL != result) {
			/* taint the memory */
			lub_heap_taint_memory(result, LUB_HEAP_TAINT_ALLOC,
					      (*words << 2));
		}
	}
	return result;
}

/*--------------------------------------------------------- */