getstk.c

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#include <xinu.h>

char *getstk(uint32 nbytes)
{
    intmask mask;                   /* Saved interrupt mask     */
    struct memblk *prev, *curr;     /* Walk through memory list */
    struct memblk *fits, *fitsprev; /* Record block that fits   */

    mask = disable();
    if (nbytes == 0)
    {
        restore(mask);
        return (char *)SYSERR;
    }

    nbytes = (uint32)roundmb(nbytes); /* Use mblock multiples   */

    prev = &memlist;
    curr = memlist.mnext;
    fits = NULL;
    fitsprev = NULL; /* Just to avoid a compiler warning */

    while (curr != NULL)
    { /* Scan entire list   */
        if (curr->mlength >= nbytes)
        {                /* Record block address    */
            fits = curr; /*   when request fits */
            fitsprev = prev;
        }
        prev = curr;
        curr = curr->mnext;
    }

    if (fits == NULL)
    { /* No block was found */
        restore(mask);
        return (char *)SYSERR;
    }
    if (nbytes == fits->mlength)
    { /* Block is exact match   */
        fitsprev->mnext = fits->mnext;
    }
    else
    { /* Remove top section */
        fits->mlength -= nbytes;
        fits = (struct memblk *)((uint32)fits + fits->mlength);
    }
    memlist.mlength -= nbytes;
    restore(mask);
    return (char *)((uint32)fits + nbytes - sizeof(uint32));
}