1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
|
(* 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.
|