freemem.c

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#include <xinu.h>

syscall freemem(char *blkaddr, uint32 nbytes)
{
    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;
}