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(* Copyright (C) 2015-2025 Free Software Foundation, Inc. *)
(* This file is part of GNU Modula-2.
GNU Modula-2 is free software; you can redistribute it and/or modify it under
the terms of the GNU General Public License as published by the Free
Software Foundation; either version 3, or (at your option) any later
version.
GNU Modula-2 is distributed in the hope that it will be useful, but WITHOUT ANY
WARRANTY; without even the implied warranty of MERCHANTABILITY or
FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License
for more details.
You should have received a copy of the GNU General Public License
along with GCC; see the file COPYING3. If not see
<http://www.gnu.org/licenses/>. *)
IMPLEMENTATION MODULE mcStack ;
FROM Storage IMPORT ALLOCATE, DEALLOCATE ;
FROM Indexing IMPORT Index, InitIndex, LowIndice, HighIndice, GetIndice, PutIndice,
DeleteIndice, KillIndex ;
TYPE
stack = POINTER TO RECORD
list : Index ;
count: CARDINAL ;
END ;
(*
init - create and return a stack.
*)
PROCEDURE init () : stack ;
VAR
s: stack ;
BEGIN
NEW (s) ;
WITH s^ DO
list := InitIndex (1) ;
count := 0
END ;
RETURN s
END init ;
(*
kill - deletes stack, s.
*)
PROCEDURE kill (VAR s: stack) ;
BEGIN
s^.list := KillIndex (s^.list) ;
DISPOSE (s) ;
s := NIL
END kill ;
(*
push - an address, a, onto the stack, s.
It returns, a.
*)
PROCEDURE push (s: stack; a: ADDRESS) : ADDRESS ;
BEGIN
WITH s^ DO
IF count=0
THEN
PutIndice (list, LowIndice (list), a)
ELSE
PutIndice (list, HighIndice (list)+1, a)
END ;
INC (count)
END ;
RETURN a
END push ;
(*
pop - and return the top element from stack, s.
*)
PROCEDURE pop (s: stack) : ADDRESS ;
VAR
a: ADDRESS ;
BEGIN
WITH s^ DO
IF count = 0
THEN
HALT
ELSE
DEC (count) ;
a := GetIndice (list, HighIndice (list)) ;
DeleteIndice (list, HighIndice (list)) ;
RETURN a
END
END
END pop ;
(*
replace - performs a pop; push (a); return a.
*)
PROCEDURE replace (s: stack; a: ADDRESS) : ADDRESS ;
VAR
b: ADDRESS ;
BEGIN
b := pop (s) ;
RETURN push (s, a)
END replace ;
(*
depth - returns the depth of the stack.
*)
PROCEDURE depth (s: stack) : CARDINAL ;
BEGIN
RETURN s^.count
END depth ;
(*
access - returns the, i, th stack element.
The top of stack is defined by:
access (s, depth (s)).
*)
PROCEDURE access (s: stack; i: CARDINAL) : ADDRESS ;
BEGIN
IF (i>s^.count) OR (i=0)
THEN
HALT
ELSE
RETURN GetIndice (s^.list, i)
END
END access ;
END mcStack.
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