src/lib/ack/libp/dis.c

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/* $Header$ */
/*
 * (c) copyright 1983 by the Vrije Universiteit, Amsterdam, The Netherlands.
 *
 *          This product is part of the Amsterdam Compiler Kit.
 *
 * Permission to use, sell, duplicate or disclose this software must be
 * obtained in writing. Requests for such permissions may be sent to
 *
 *      Dr. Andrew S. Tanenbaum
 *      Wiskundig Seminarium
 *      Vrije Universiteit
 *      Postbox 7161
 *      1007 MC Amsterdam
 *      The Netherlands
 *
 */

/* Author: J.W. Stevenson */

#include        <pc_err.h>

#define assert()        /* nothing */

/*
 * use circular list of free blocks from low to high addresses
 * _highp points to free block with highest address
 */
struct adm {
        struct adm      *next;
        int             size;
};

extern struct adm       *_lastp;
extern struct adm       *_highp;
extern                  _trp();

static int merge(p1,p2) struct adm *p1,*p2; {
        struct adm *p;

        p = (struct adm *)((char *)p1 + p1->size);
        if (p > p2)
                _trp(EFREE);
        if (p != p2)
                return(0);
        p1->size += p2->size;
        p1->next = p2->next;
        return(1);
}

_dis(n,pp) int n; struct adm **pp; {
        struct adm *p1,*p2;

        /*
         * NOTE: dispose only objects whose size is a multiple of sizeof(*pp).
         *       this is always true for objects allocated by _new()
         */
        n = ((n+sizeof(*p1)-1) / sizeof(*p1)) * sizeof(*p1);
        if (n == 0)
                return;
        if ((p1= *pp) == (struct adm *) 0)
                _trp(EFREE);
        p1->size = n;
        if ((p2 = _highp) == 0)  /*p1 is the only free block*/
                p1->next = p1;
        else {
                if (p2 > p1) {
                        /*search for the preceding free block*/
                        if (_lastp < p1)  /*reduce search*/
                                p2 = _lastp;
                        while (p2->next < p1)
                                p2 = p2->next;
                }
                /* if p2 preceeds p1 in the circular list,
                 * try to merge them                    */
                p1->next = p2->next; p2->next = p1;
                if (p2 <= p1 && merge(p2,p1))
                        p1 = p2;
                p2 = p1->next;
                /* p1 preceeds p2 in the circular list */
                if (p2 > p1) merge(p1,p2);
        }
        if (p1 >= p1->next)
                _highp = p1;
        _lastp = p1;
        *pp = (struct adm *) 0;
}

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