/* freemem.c - freemem */

#include 

/*------------------------------------------------------------------------
 *  freemem  -  Free a memory block, returning the block to the free list
 *------------------------------------------------------------------------
 */
syscall freemem(
          char          *blkaddr,       /* Pointer to memory block      */
          uint32        nbytes          /* Size of block in bytes       */
        )
{
        intmask mask;                   /* Saved interrupt mask         */
        struct  memblk  *next, *prev, *block;
        uint32  top;

        mask = disable();
        if ((nbytes == 0) || ((uint32) blkaddr < (uint32) minheap)
                          || ((uint32) blkaddr > (uint32) maxheap)) {
                restore(mask);
                return SYSERR;
        }

        nbytes = (uint32) roundmb(nbytes);      /* Use memblk multiples */
        block = (struct memblk *)blkaddr;

        prev = &memlist;                        /* Walk along free list */
        next = memlist.mnext;
        while ((next != NULL) && (next < block)) {
                prev = next;
                next = next->mnext;
        }

        if (prev == &memlist) {         /* Compute top of previous block*/
                top = (uint32) NULL;
        } else {
                top = (uint32) prev + prev->mlength;
        }

        /* Ensure new block does not overlap previous or next blocks    */

        if (((prev != &memlist) && (uint32) block < top)
            || ((next != NULL)  && (uint32) block+nbytes>(uint32)next)) {
                restore(mask);
                return SYSERR;
        }

        memlist.mlength += nbytes;

        /* Either coalesce with previous block or add to free list */

        if (top == (uint32) block) {    /* Coalesce with previous block */
                prev->mlength += nbytes;
                block = prev;
        } else {                        /* Link into list as new node   */
                block->mnext = next;
                block->mlength = nbytes;
                prev->mnext = block;
        }

        /* Coalesce with next block if adjacent */

        if (((uint32) block + block->mlength) == (uint32) next) {
                block->mlength += next->mlength;
                block->mnext = next->mnext;
        }
        restore(mask);
        return OK;
}