#include "mpool.h"

/*
 * инициализация пула
 */
void mpool_init(struct mpool_s *bp, size_t nblocks, size_t mpool_block_size)
{
	size_t i;

	bp->nblocks = nblocks;

	mpool_block_size += 2 * sizeof(struct mpool_block_s *);

	bp->pool = (struct mpool_block_s *)malloc(nblocks * mpool_block_size);

	if (!bp->pool)
	    fatal("virtual memory exhaused");

	void *p = bp->pool + mpool_block_size,
	     *pmax = p + (nblocks - 2) * mpool_block_size;

	for ( ; p < pmax; p += mpool_block_size) {
		((struct mpool_block_s *)p)->prev = (struct mpool_block_s *)(p - mpool_block_size);
		((struct mpool_block_s *)p)->next = (struct mpool_block_s *)(p + mpool_block_size);
	}

	((struct mpool_block_s *)bp->pool)->prev = NULL;
	((struct mpool_block_s *)bp->pool)->next = (struct mpool_block_s *)(bp->pool + mpool_block_size);

	((struct mpool_block_s *)(bp->pool + (nblocks - 1) * mpool_block_size))->prev =
		(struct mpool_block_s *)(bp->pool + (nblocks - 2) * mpool_block_size);
	((struct mpool_block_s *)(bp->pool + (nblocks - 1) * mpool_block_size))->next = NULL;

	bp->free_pool = (struct mpool_block_s *)bp->pool;
	bp->busy_pool = NULL;
}

/*
 * уничтожение пула
 */
void mpool_destroy(struct mpool_s *bp)
{
	free(bp->pool);
	bp->nblocks = 0;
	bp->pool = bp->free_pool = bp->busy_pool = NULL;
}

/*
 * выдача блока из пула
 */
void *mpool_alloc(struct mpool_s *bp)
{
	if (!bp->free_pool)
		return NULL;

	bp->free_pool->prev = bp->free_pool->next; // save free_pool->next in free_pool->prev
	
	bp->free_pool->next = bp->busy_pool;

	if (bp->busy_pool)
		bp->busy_pool->prev = bp->free_pool;

	bp->busy_pool = bp->free_pool;

	bp->free_pool = bp->free_pool->prev;
	
	bp->busy_pool->prev = NULL; // saved in free_pool->prev to NULL

	return &bp->busy_pool->obj;
}

/*
 * возвращение блока в пул
 */
void mpool_free(struct mpool_s *bp, void *p)
{
	if (!p)
		return;

	struct mpool_block_s *b1 = (struct mpool_block_s *)(p - 2 * sizeof(struct mpool_block_s *)),
		       *b2 = b1->next;

	if (b1->prev)
		b1->prev->next = b2;
	if (b2)
		b2->prev = b1->prev;

	if (bp->free_pool) {
		b1->next = bp->free_pool;
		bp->free_pool->prev = b1;
	}
	else
		b1->next = NULL;

	bp->free_pool = b2;

	if (bp->busy_pool == b1)
		bp->busy_pool = b2;
}