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
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162
163
164
165
166
167
168
169
170
171
172
173
174
175
176
177
178
179
180
181
182
183
184
185
186
|
/* vi: set sw=4 ts=4: */
#include "busybox.h"
#include <ctype.h>
#include <stdio.h>
#include <stdlib.h>
#include <unistd.h>
#include <math.h>
/* Tiny RPN calculator, because "expr" didn't give me bitwise operations. */
static double stack[100];
static unsigned int pointer;
static void push(double a)
{
if (pointer >= (sizeof(stack) / sizeof(*stack))) {
errorMsg("stack overflow\n");
exit(-1);
} else
stack[pointer++] = a;
}
static double pop()
{
if (pointer == 0) {
errorMsg("stack underflow\n");
exit(-1);
}
return stack[--pointer];
}
static void add()
{
push(pop() + pop());
}
static void sub()
{
double subtrahend = pop();
push(pop() - subtrahend);
}
static void mul()
{
push(pop() * pop());
}
static void divide()
{
double divisor = pop();
push(pop() / divisor);
}
static void and()
{
push((unsigned int) pop() & (unsigned int) pop());
}
static void or()
{
push((unsigned int) pop() | (unsigned int) pop());
}
static void eor()
{
push((unsigned int) pop() ^ (unsigned int) pop());
}
static void not()
{
push(~(unsigned int) pop());
}
static void print()
{
printf("%g\n", pop());
}
struct op {
const char *name;
void (*function) ();
};
static const struct op operators[] = {
{"+", add},
{"add", add},
{"-", sub},
{"sub", sub},
{"*", mul},
{"mul", mul},
{"/", divide},
{"div", divide},
{"and", and},
{"or", or},
{"not", not},
{"eor", eor},
{0, 0}
};
static void stack_machine(const char *argument)
{
char *endPointer = 0;
double d;
const struct op *o = operators;
if (argument == 0) {
print();
return;
}
d = strtod(argument, &endPointer);
if (endPointer != argument) {
push(d);
return;
}
while (o->name != 0) {
if (strcmp(o->name, argument) == 0) {
(*(o->function)) ();
return;
}
o++;
}
errorMsg("%s: syntax error.\n", argument);
exit(-1);
}
/* return pointer to next token in buffer and set *buffer to one char
* past the end of the above mentioned token
*/
static char *get_token(char **buffer)
{
char *start = NULL;
char *current = *buffer;
while (isspace(*current)) { current++; }
if (*current != 0) {
start = current;
while (!isspace(*current) && current != 0) { current++; }
*buffer = current;
}
return start;
}
/* In Perl one might say, scalar m|\s*(\S+)\s*|g */
static int number_of_tokens(char *buffer)
{
int i = 0;
char *b = buffer;
while (get_token(&b)) { i++; }
return i;
}
int dc_main(int argc, char **argv)
{
/* take stuff from stdin if no args are given */
if (argc <= 1) {
int i, len;
char *line = NULL;
char *cursor = NULL;
char *token = NULL;
while ((line = get_line_from_file(stdin))) {
cursor = line;
len = number_of_tokens(line);
for (i = 0; i < len; i++) {
token = get_token(&cursor);
*cursor++ = 0;
stack_machine(token);
}
free(line);
}
} else {
if (*argv[1]=='-')
usage(dc_usage);
while (argc >= 2) {
stack_machine(argv[1]);
argv++;
argc--;
}
}
stack_machine(0);
return( TRUE);
}
|
