87 lines
1.9 KiB
C
87 lines
1.9 KiB
C
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/*
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* (c) copyright 1983 by the Vrije Universiteit, Amsterdam, The Netherlands.
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*
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* This product is part of the Amsterdam Compiler Kit.
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*
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* Permission to use, sell, duplicate or disclose this software must be
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* obtained in writing. Requests for such permissions may be sent to
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*
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* Dr. Andrew S. Tanenbaum
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* Wiskundig Seminarium
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* Vrije Universiteit
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* Postbox 7161
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* 1007 MC Amsterdam
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* The Netherlands
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*
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*/
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/* Author: J.W. Stevenson */
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#include <pc_err.h>
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#define assert() /* nothing */
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/*
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* use circular list of free blocks from low to high addresses
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* _highp points to free block with highest address
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*/
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struct adm {
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struct adm *next;
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int size;
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};
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extern struct adm *_lastp;
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extern struct adm *_highp;
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extern _trp();
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static int merge(p1,p2) struct adm *p1,*p2; {
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struct adm *p;
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p = (struct adm *)((char *)p1 + p1->size);
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if (p > p2)
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_trp(EFREE);
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if (p != p2)
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return(0);
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p1->size += p2->size;
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p1->next = p2->next;
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return(1);
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}
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_dis(n,pp) int n; struct adm **pp; {
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struct adm *p1,*p2;
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/*
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* NOTE: dispose only objects whose size is a multiple of sizeof(*pp).
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* this is always true for objects allocated by _new()
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*/
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n = ((n+sizeof(*p1)-1) / sizeof(*p1)) * sizeof(*p1);
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if (n == 0)
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return;
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if ((p1= *pp) == (struct adm *) 0)
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_trp(EFREE);
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p1->size = n;
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if ((p2 = _highp) == 0) /*p1 is the only free block*/
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p1->next = p1;
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else {
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if (p2 > p1) {
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/*search for the preceding free block*/
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if (_lastp < p1) /*reduce search*/
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p2 = _lastp;
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while (p2->next < p1)
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p2 = p2->next;
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}
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/* if p2 preceeds p1 in the circular list,
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* try to merge them */
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p1->next = p2->next; p2->next = p1;
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if (p2 <= p1 && merge(p2,p1))
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p1 = p2;
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p2 = p1->next;
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/* p1 preceeds p2 in the circular list */
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if (p2 > p1) merge(p1,p2);
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}
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if (p1 >= p1->next)
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_highp = p1;
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_lastp = p1;
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*pp = (struct adm *) 0;
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}
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