minix/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;
}