getmem.c

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#include <xinu.h>

char *getmem(uint32 nbytes)
{
    intmask mask; /* Saved interrupt mask       */
    struct memblk *prev, *curr, *leftover;

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

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

    prev = &memlist;
    curr = memlist.mnext;
    while (curr != NULL)
    { /* Search free list   */

        if (curr->mlength == nbytes)
        { /* Block is exact match   */
            prev->mnext = curr->mnext;
            memlist.mlength -= nbytes;
            restore(mask);
            return (char *)(curr);
        }
        else if (curr->mlength > nbytes)
        { /* Split big block    */
            leftover = (struct memblk *)((uint32)curr +
                                         nbytes);
            prev->mnext = leftover;
            leftover->mnext = curr->mnext;
            leftover->mlength = curr->mlength - nbytes;
            memlist.mlength -= nbytes;
            restore(mask);
            return (char *)(curr);
        }
        else
        { /* Move to next block */
            prev = curr;
            curr = curr->mnext;
        }
    }
    restore(mask);
    return (char *)SYSERR;
}