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/*
 * free.c
 *
 * Very simple linked-list based malloc()/free().
 */

#include <stdlib.h>
#include "malloc.h"

static struct free_arena_header *
        __free_block(struct free_arena_header *ah) {
    struct free_arena_header *pah, *nah;

    pah = ah->a.prev;
    nah = ah->a.next;
    if ( ARENA_TYPE_GET(pah->a.attrs) == ARENA_TYPE_FREE &&
           (char *)pah+ARENA_SIZE_GET(pah->a.attrs) == (char *)ah ) {
        /* Coalesce into the previous block */
        ARENA_SIZE_SET(pah->a.attrs, ARENA_SIZE_GET(pah->a.attrs) +
    		ARENA_SIZE_GET(ah->a.attrs));
        pah->a.next = nah;
        nah->a.prev = pah;

#ifdef DEBUG_MALLOC
        ARENA_TYPE_SET(ah->a.attrs, ARENA_TYPE_DEAD);
#endif

        ah = pah;
        pah = ah->a.prev;
    } else {
        /* Need to add this block to the free chain */
        ARENA_TYPE_SET(ah->a.attrs, ARENA_TYPE_FREE);
        ah->a.tag = NULL;

        ah->next_free = __malloc_head.next_free;
        ah->prev_free = &__malloc_head;
        __malloc_head.next_free = ah;
        ah->next_free->prev_free = ah;
    }

    /* In either of the previous cases, we might be able to merge
       with the subsequent block... */
    if ( ARENA_TYPE_GET(nah->a.attrs) == ARENA_TYPE_FREE &&
           (char *)ah+ARENA_SIZE_GET(ah->a.attrs) == (char *)nah ) {
        ARENA_SIZE_SET(ah->a.attrs, ARENA_SIZE_GET(ah->a.attrs) +
    		ARENA_SIZE_GET(nah->a.attrs));

        /* Remove the old block from the chains */
        nah->next_free->prev_free = nah->prev_free;
        nah->prev_free->next_free = nah->next_free;
        ah->a.next = nah->a.next;
        nah->a.next->a.prev = ah;

#ifdef DEBUG_MALLOC
        ARENA_TYPE_SET(nah->a.attrs, ARENA_TYPE_DEAD);
#endif
    }

    /* Return the block that contains the called block */
    return ah;
}

void free(void *ptr)
{
    struct free_arena_header *ah;

    if ( !ptr )
        return;

    ah = (struct free_arena_header *)
        ((struct arena_header *)ptr - 1);

#ifdef DEBUG_MALLOC
    assert( ARENA_TYPE_GET(ah->a.attrs) == ARENA_TYPE_USED );
#endif

    __free_block(ah);

  /* Here we could insert code to return memory to the system. */
}

/*
 * This is used to insert a block which is not previously on the
 * free list.  Only the a.size field of the arena header is assumed
 * to be valid.
 */
void __inject_free_block(struct free_arena_header *ah)
{
    struct free_arena_header *nah;
    size_t a_end = (size_t) ah + ARENA_SIZE_GET(ah->a.attrs);
    size_t n_end;

    for (nah = __malloc_head.a.next; ARENA_TYPE_GET(nah->a.attrs) != ARENA_TYPE_HEAD;
         nah = nah->a.next) {
        n_end = (size_t) nah + ARENA_SIZE_GET(nah->a.attrs);

        /* Is nah entirely beyond this block? */
        if ((size_t) nah >= a_end)
            break;

        /* Is this block entirely beyond nah? */
        if ((size_t) ah >= n_end)
            continue;

        /* Otherwise we have some sort of overlap - reject this block */
        return;
    }

    /* Now, nah should point to the successor block */
    ah->a.next = nah;
    ah->a.prev = nah->a.prev;
    nah->a.prev = ah;
    ah->a.prev->a.next = ah;

    __free_block(ah);
}


void __free_tagged(void *tag) {
	struct free_arena_header *fp, *nfp;

	for (fp = __malloc_head.a.next, nfp = fp->a.next;
			ARENA_TYPE_GET(fp->a.attrs) != ARENA_TYPE_HEAD;
			fp = nfp, nfp = fp->a.next) {

		if (ARENA_TYPE_GET(fp->a.attrs) == ARENA_TYPE_USED &&
				fp->a.tag == tag) {
			// Free this block
			__free_block(fp);
		}
	}
}