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
|
#include <stdlib.h>
#include <ctype.h>
/*
grammar:
Start = Expr ';'
Expr = Or | Or '?' Expr ':' Expr
Or = And | Or '||' And
And = Eq | And '&&' Eq
Eq = Rel | Eq '==' Rel | Eq '!=' Rel
Rel = Add | Rel '<=' Add | Rel '>=' Add | Rel '<' Add | Rel '>' Add
Add = Mul | Add '+' Mul | Add '-' Mul
Mul = Term | Mul '*' Term | Mul '/' Term | Mul '%' Term
Term = '(' Expr ')' | '!' Term | decimal | 'n'
internals:
recursive descent expression evaluator with stack depth limit.
eval* functions return the value of the subexpression and set
the current string pointer to the next non-space char.
*/
struct st {
const char *s;
unsigned long n;
int err;
};
static const char *skipspace(const char *s)
{
while (isspace(*s)) s++;
return s;
}
static unsigned long fail(struct st *st)
{
st->err = 1;
return 0;
}
static unsigned long evalexpr(struct st *st, int d);
static unsigned long evalterm(struct st *st, int d)
{
unsigned long a;
char *e;
if (--d < 0) return fail(st);
st->s = skipspace(st->s);
if (isdigit(*st->s)) {
a = strtoul(st->s, &e, 10);
if (e == st->s || a == -1) return fail(st);
st->s = skipspace(e);
return a;
}
if (*st->s == 'n') {
st->s = skipspace(st->s + 1);
return st->n;
}
if (*st->s == '(') {
st->s++;
a = evalexpr(st, d);
if (*st->s != ')') return fail(st);
st->s = skipspace(st->s + 1);
return a;
}
if (*st->s == '!') {
st->s++;
return !evalterm(st, d);
}
return fail(st);
}
static unsigned long evalmul(struct st *st, int d)
{
unsigned long b, a = evalterm(st, d);
int op;
for (;;) {
op = *st->s;
if (op != '*' && op != '/' && op != '%')
return a;
st->s++;
b = evalterm(st, d);
if (op == '*') {
a *= b;
} else if (!b) {
return fail(st);
} else if (op == '%') {
a %= b;
} else {
a /= b;
}
}
}
static unsigned long evaladd(struct st *st, int d)
{
unsigned long a = 0;
int sub = 0;
for (;;) {
a += (sub ? -1 : 1) * evalmul(st, d);
if (*st->s != '+' && *st->s != '-')
return a;
sub = *st->s == '-';
st->s++;
}
}
static unsigned long evalrel(struct st *st, int d)
{
unsigned long b, a = evaladd(st, d);
int less, eq;
for (;;) {
if (*st->s != '<' && *st->s != '>')
return a;
less = st->s[0] == '<';
eq = st->s[1] == '=';
st->s += 1 + eq;
b = evaladd(st, d);
a = (less ? a < b : a > b) || (eq && a == b);
}
}
static unsigned long evaleq(struct st *st, int d)
{
unsigned long a = evalrel(st, d);
int c;
for (;;) {
c = st->s[0];
if ((c != '=' && c != '!') || st->s[1] != '=')
return a;
st->s += 2;
a = (evalrel(st, d) == a) ^ (c == '!');
}
}
static unsigned long evaland(struct st *st, int d)
{
unsigned long a = evaleq(st, d);
for (;;) {
if (st->s[0] != '&' || st->s[1] != '&')
return a;
st->s += 2;
a = evaleq(st, d) && a;
}
}
static unsigned long evalor(struct st *st, int d)
{
unsigned long a = evaland(st, d);
for (;;) {
if (st->s[0] != '|' || st->s[1] != '|')
return a;
st->s += 2;
a = evaland(st, d) || a;
}
}
static unsigned long evalexpr(struct st *st, int d)
{
unsigned long a1, a2, a3;
if (--d < 0)
return fail(st);
a1 = evalor(st, d-6);
if (*st->s != '?')
return a1;
st->s++;
a2 = evalexpr(st, d);
if (*st->s != ':')
return fail(st);
st->s++;
a3 = evalexpr(st, d);
return a1 ? a2 : a3;
}
unsigned long __pleval(const char *s, unsigned long n)
{
unsigned long a;
struct st st;
st.s = s;
st.n = n;
st.err = 0;
a = evalexpr(&st, 100);
if (st.err || *st.s != ';')
return -1;
return a;
}
|
