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
187
188
189
190
191
192
193
194
195
196
197
198
199
200
201
202
203
204
205
206
207
208
209
210
211
212
213
214
215
216
217
218
219
220
221
222
223
224
225
226
227
228
229
230
231
232
233
234
235
236
237
238
239
240
241
242
243
244
245
246
247
248
249
250
251
252
253
254
255
256
257
258
259
260
261
262
263
264
265
266
267
268
269
270
271
272
273
274
275
276
277
278
279
280
281
282
283
284
285
286
287
288
289
290
291
292
|
/*
* File: strexpr.c
* Purpose: calculate value from algebraic string expression
* (Stripped down from expr.c from J.T. Conklin <jtc@netbsd.org>.)
* Version: 1.0 (Nov 1995)
* Author: Piet Tutelaers
*/
#include <stdio.h> /* sprintf() */
#include <stdlib.h> /* free(), malloc() */
#include <string.h> /* strchr(), strcpy() */
#include <ctype.h> /* isdigit(), isspace() */
#include "basics.h" /* fatal() */
const char *OPERATORS = "+-*/%()";
enum token {
ADD, SUB, MUL, DIV, MOD, LP, RP, OPERAND, EOI
};
struct val {
enum {
integer,
string
} type;
union {
char *s;
int i;
} u;
};
enum token token;
struct val *tokval;
char *pexpr;
struct val *
make_int(int i)
{
struct val *vp;
vp = (struct val *) malloc(sizeof(*vp));
if (vp == NULL) fatal("expression error\n");
vp->type = integer;
vp->u.i = i;
return vp;
}
struct val *
make_str(char *s)
{
char operand[32]; int i;
struct val *vp;
vp = (struct val *) malloc(sizeof(*vp));
if (vp == NULL) fatal("expression error\n");
pexpr = s; i = 0;
while (1) {
if (isspace(*pexpr) || *pexpr == '\0') break;
if (strchr(OPERATORS, *pexpr) != NULL) break;
if (i == 30) fatal("operand too large\n");
operand[i++] = *pexpr++;
}
if (i == 0) fatal("invalid operand\n");
operand[i] = '\0';
vp->u.s = malloc(i+1);
if (vp->u.s == NULL) fatal("Out of memory\n");
strcpy(vp->u.s, operand);
vp->type = string;
return vp;
}
void
free_value(struct val *vp)
{
if (vp->type == string)
free(vp->u.s);
free(vp);
}
/* determine if vp is an integer; if so, return it's value in *r */
int
is_integer(struct val *vp, int *r)
{
char *s;
int neg;
int i;
if (vp->type == integer) {
*r = vp->u.i;
return 1;
}
/*
* POSIX.2 defines an "integer" as an optional unary minus
* followed by digits.
*/
s = vp->u.s;
i = 0;
neg = (*s == '-');
if (neg)
s++;
while (*s) {
if (!isdigit(*s))
return 0;
i *= 10;
i += *s - '0';
s++;
}
if (neg)
i *= -1;
*r = i;
return 1;
}
/* coerce to vp to an integer */
int
to_integer(struct val *vp)
{
int r;
if (vp->type == integer)
return 1;
if (is_integer(vp, &r)) {
free(vp->u.s);
vp->u.i = r;
vp->type = integer;
return 1;
}
return 0;
}
/* coerce to vp to an string */
void
to_string(struct val *vp)
{
char *tmp;
if (vp->type == string)
return;
tmp = malloc(25);
if (tmp == NULL) fatal("Out of memory\n");
sprintf(tmp, "%d", vp->u.i);
vp->type = string;
vp->u.s = tmp;
}
void
nexttoken()
{
char *i; /* index */
while (isspace(*pexpr)) pexpr++;
if (*pexpr == '\0') {
token = EOI;
return;
}
if ((i = strchr(OPERATORS, *pexpr)) != NULL) {
pexpr++;
token = i - OPERATORS;
return;
}
tokval = make_str(pexpr);
token = OPERAND;
return;
}
struct val *
eval6()
{
struct val *eval3(void);
struct val *v;
if (token == OPERAND) {
nexttoken();
return tokval;
} else if (token == LP) {
nexttoken();
v = eval3();
if (token != RP)
fatal("missing parenthesis in expression\n");
nexttoken();
return v;
} else fatal("expression error\n");
/* NOTREACHED */
}
/* Parse and evaluate multiplication and division expressions */
struct val *
eval4()
{
struct val *l, *r;
enum token op;
l = eval6();
while ((op = token) == MUL || op == DIV || op == MOD) {
nexttoken();
r = eval6();
if (!to_integer(l) || !to_integer(r)) {
fatal("non-numeric argument\n");
}
if (op == MUL) {
l->u.i *= r->u.i;
} else {
if (r->u.i == 0) {
fatal("division by zero\n");
}
if (op == DIV) {
l->u.i /= r->u.i;
} else {
l->u.i %= r->u.i;
}
}
free_value(r);
}
return l;
}
/* Parse and evaluate addition and subtraction expressions */
struct val *
eval3()
{
struct val *l, *r;
enum token op;
l = eval4();
while ((op = token) == ADD || op == SUB) {
nexttoken();
r = eval4();
if (!to_integer(l) || !to_integer(r)) {
fatal("non-numeric argument\n");
}
if (op == ADD) {
l->u.i += r->u.i;
} else {
l->u.i -= r->u.i;
}
free_value(r);
}
return l;
}
/*
* Evaluate the algebraic expression contained in <expression>. The
* value will be assigned to <result>. When errors are encountered
* non-zero is returned (if program is not aborted) otherwise zero.
*/
int strexpr(int *result, char *expression) {
struct val *vp;
pexpr = expression;
nexttoken();
vp = eval3();
if (token != EOI) return 1;
if (vp->type == integer || to_integer(vp)) {
*result = vp->u.i;
return 0;
}
return 1;
}
|
