300 lines
6.1 KiB
Modula-2
300 lines
6.1 KiB
Modula-2
(*
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(c) copyright 1988 by the Vrije Universiteit, Amsterdam, The Netherlands.
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See the copyright notice in the ACK home directory, in the file "Copyright".
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*)
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(*$R-*)
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IMPLEMENTATION MODULE Storage;
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(*
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Module: Dynamic Storage Allocation
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Author: Ceriel J.H. Jacobs
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Adapted from a version in C by Hans Tebra
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Version: $Header$
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*)
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(* This storage manager maintains an array of lists of objects with the
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same size. Commonly used sizes have their own bucket. The larger ones
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are put in a single list.
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*)
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FROM Unix IMPORT sbrk, ILLBREAK;
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FROM SYSTEM IMPORT ADDRESS, ADR;
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FROM Traps IMPORT Message;
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CONST
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NLISTS = 20;
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TYPE
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ALIGNTYPE =
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RECORD
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CASE : INTEGER OF
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1: l: LONGINT |
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2: p: ADDRESS |
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3: d: LONGREAL
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END
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END; (* A type with high alignment requirements *)
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BucketPtr = POINTER TO Bucket;
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Bucket =
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RECORD
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CASE : BOOLEAN OF
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FALSE: BSIZE: CARDINAL; (* size of user part in UNITs *)
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BNEXT: BucketPtr; | (* next free Bucket *)
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TRUE: BXX: ALIGNTYPE
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END;
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BSTORE: ALIGNTYPE;
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END;
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CONST
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UNIT = SIZE(ALIGNTYPE);
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VAR
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FreeLists: ARRAY[0..NLISTS] OF BucketPtr; (* small blocks *)
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Llist: BucketPtr; (* others *)
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Compacted: BOOLEAN; (* avoid recursive reorganization *)
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FirstBlock: BucketPtr;
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USED: ADDRESS;
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PROCEDURE MyAllocate(size: CARDINAL) : ADDRESS;
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VAR nu : CARDINAL;
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b : CARDINAL;
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p, q: BucketPtr;
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brk : ADDRESS;
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BEGIN
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nu := (size + (UNIT-1)) DIV UNIT;
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IF nu = 0 THEN
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RETURN NIL;
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END;
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IF nu <= NLISTS THEN
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b := nu;
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IF FreeLists[b] # NIL THEN
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(* Exact fit *)
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p := FreeLists[b];
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FreeLists[b] := p^.BNEXT;
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p^.BNEXT := USED;
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RETURN ADR(p^.BSTORE);
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END;
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(* Search for a block with >= 2 units more than requested.
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We pay for an additional header when the block is split.
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*)
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FOR b := b+2 TO NLISTS DO
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IF FreeLists[b] # NIL THEN
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q := FreeLists[b];
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FreeLists[b] := q^.BNEXT;
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p := ADDRESS(q) + (nu+1)*UNIT;
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(* p indicates the block that must be given
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back
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*)
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p^.BSIZE := q^.BSIZE - nu - 1;
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p^.BNEXT := FreeLists[p^.BSIZE];
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FreeLists[p^.BSIZE] := p;
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q^.BSIZE := nu;
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q^.BNEXT := USED;
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RETURN ADR(q^.BSTORE);
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END;
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END;
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END;
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p := Llist;
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IF p # NIL THEN
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q := NIL;
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WHILE (p # NIL) AND (p^.BSIZE < nu) DO
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q := p;
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p := p^.BNEXT;
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END;
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IF p # NIL THEN
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(* p^.BSIZE >= nu *)
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IF p^.BSIZE <= nu + NLISTS + 1 THEN
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(* Remove p from this list *)
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IF q # NIL THEN q^.BNEXT := p^.BNEXT
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ELSE Llist := p^.BNEXT;
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END;
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p^.BNEXT := USED;
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IF p^.BSIZE > nu + 1 THEN
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(* split block,
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tail goes to FreeLists area
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*)
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q := ADDRESS(p) + (nu+1)*UNIT;
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q^.BSIZE := p^.BSIZE -nu -1;
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q^.BNEXT := FreeLists[q^.BSIZE];
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FreeLists[q^.BSIZE] := q;
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p^.BSIZE := nu;
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END;
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RETURN ADR(p^.BSTORE);
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END;
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(* Give part of tail of original block.
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Block stays in this list.
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*)
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q := ADDRESS(p) + (p^.BSIZE-nu)*UNIT;
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q^.BSIZE := nu;
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p^.BSIZE := p^.BSIZE - nu - 1;
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q^.BNEXT := USED;
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RETURN ADR(q^.BSTORE);
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END;
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END;
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IF Compacted THEN
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(* reorganization did not yield sufficient memory *)
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RETURN NIL;
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END;
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brk := sbrk(UNIT * (nu + 1));
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IF brk = ILLBREAK THEN
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ReOrganize();
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Compacted := TRUE;
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brk := MyAllocate(size);
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Compacted := FALSE;
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RETURN brk;
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END;
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p := brk;
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p^.BSIZE := nu;
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p^.BNEXT := USED;
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RETURN ADR(p^.BSTORE);
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END MyAllocate;
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PROCEDURE Allocate(VAR a: ADDRESS; size: CARDINAL);
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BEGIN
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ALLOCATE(a, size);
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END Allocate;
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PROCEDURE ALLOCATE(VAR a: ADDRESS; size: CARDINAL);
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BEGIN
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a := MyAllocate(size);
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IF a = NIL THEN
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Message("out of core");
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HALT;
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END;
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END ALLOCATE;
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PROCEDURE Available(size: CARDINAL): BOOLEAN;
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VAR a: ADDRESS;
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BEGIN
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a:= MyAllocate(size);
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IF a # NIL THEN
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DEALLOCATE(a, size);
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RETURN TRUE;
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END;
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RETURN FALSE;
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END Available;
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PROCEDURE Deallocate(VAR a: ADDRESS; size: CARDINAL);
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BEGIN
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DEALLOCATE(a, size);
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END Deallocate;
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PROCEDURE DEALLOCATE(VAR a: ADDRESS; size: CARDINAL);
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VAR p: BucketPtr;
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BEGIN
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IF (a = NIL) THEN RETURN; END;
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p := a - UNIT;
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IF (p^.BNEXT # BucketPtr(USED)) THEN RETURN; END;
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WITH p^ DO
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IF BSIZE <= NLISTS THEN
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BNEXT := FreeLists[BSIZE];
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FreeLists[BSIZE] := p;
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ELSE
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BNEXT := Llist;
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Llist := p;
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END;
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END;
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END DEALLOCATE;
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PROCEDURE ReOrganize();
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VAR lastblock: BucketPtr;
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b, be: BucketPtr;
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i: CARDINAL;
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BEGIN
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lastblock := NIL;
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FOR i := 1 TO NLISTS DO
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b := FreeLists[i];
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WHILE b # NIL DO
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IF ADDRESS(b) > ADDRESS(lastblock) THEN
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lastblock := b;
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END;
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be := b^.BNEXT;
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b^.BNEXT := NIL; (* temporary free mark *)
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b := be;
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END;
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END;
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b := Llist;
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WHILE b # NIL DO
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IF ADDRESS(b) > ADDRESS(lastblock) THEN
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lastblock := b;
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END;
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be := b^.BNEXT;
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b^.BNEXT := NIL;
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b := be;
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END;
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(* Now, all free blocks have b^.BNEXT = NIL *)
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b := FirstBlock;
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WHILE ADDRESS(b) < ADDRESS(lastblock) DO
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LOOP
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be := ADDRESS(b)+(b^.BSIZE+1)*UNIT;
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IF b^.BNEXT # NIL THEN
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(* this block is not free *)
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EXIT;
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END;
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IF ADDRESS(be) > ADDRESS(lastblock) THEN
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(* no next block *)
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EXIT;
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END;
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IF be^.BNEXT # NIL THEN
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(* next block is not free *)
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EXIT;
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END;
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(* this block and the next one are free,
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so merge them, but only if it is not too big
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*)
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IF MAX(CARDINAL) - b^.BSIZE > be^.BSIZE THEN
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b^.BSIZE := b^.BSIZE + be^.BSIZE + 1;
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ELSE
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EXIT;
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END;
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END;
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b := be;
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END;
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(* clear all free lists *)
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FOR i := 1 TO NLISTS DO FreeLists[i] := NIL; END;
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Llist := NIL;
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(* collect free blocks in them again *)
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b := FirstBlock;
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WHILE ADDRESS(b) <= ADDRESS(lastblock) DO
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WITH b^ DO
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IF BNEXT = NIL THEN
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IF BSIZE <= NLISTS THEN
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BNEXT := FreeLists[BSIZE];
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FreeLists[BSIZE] := b;
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ELSE
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BNEXT := Llist;
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Llist := b;
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END;
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END;
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END;
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b := ADDRESS(b) + (b^.BSIZE+1) * UNIT;
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END;
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END ReOrganize;
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PROCEDURE InitStorage();
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VAR i: CARDINAL;
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brk: ADDRESS;
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BEGIN
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FOR i := 1 TO NLISTS DO
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FreeLists[i] := NIL;
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END;
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Llist := NIL;
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brk := sbrk(0);
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brk := sbrk(UNIT - brk MOD UNIT);
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FirstBlock := sbrk(0);
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Compacted := FALSE;
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USED := 1;
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END InitStorage;
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BEGIN
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InitStorage();
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END Storage.
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