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
|
#include <stdlib.h>
#include <ctype.h>
#include "pleval.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 = Prim | Mul '*' Prim | Mul '/' Prim | Mul '%' Prim
Prim = '(' Expr ')' | '!' Prim | decimal | 'n'
internals:
recursive descent expression evaluator with stack depth limit.
for binary operators an operator-precedence parser is used.
eval* functions store the result of the parsed subexpression
and return a pointer to the next non-space character.
*/
struct st {
unsigned long r;
unsigned long n;
int op;
};
static const char *skipspace(const char *s)
{
while (isspace(*s)) s++;
return s;
}
static const char *evalexpr(struct st *st, const char *s, int d);
static const char *evalprim(struct st *st, const char *s, int d)
{
char *e;
if (--d < 0) return "";
s = skipspace(s);
if (isdigit(*s)) {
st->r = strtoul(s, &e, 10);
if (e == s || st->r == -1) return "";
return skipspace(e);
}
if (*s == 'n') {
st->r = st->n;
return skipspace(s+1);
}
if (*s == '(') {
s = evalexpr(st, s+1, d);
if (*s != ')') return "";
return skipspace(s+1);
}
if (*s == '!') {
s = evalprim(st, s+1, d);
st->r = !st->r;
return s;
}
return "";
}
static int binop(struct st *st, int op, unsigned long left)
{
unsigned long a = left, b = st->r;
switch (op) {
case 0: st->r = a||b; return 0;
case 1: st->r = a&&b; return 0;
case 2: st->r = a==b; return 0;
case 3: st->r = a!=b; return 0;
case 4: st->r = a>=b; return 0;
case 5: st->r = a<=b; return 0;
case 6: st->r = a>b; return 0;
case 7: st->r = a<b; return 0;
case 8: st->r = a+b; return 0;
case 9: st->r = a-b; return 0;
case 10: st->r = a*b; return 0;
case 11: if (b) {st->r = a%b; return 0;} return 1;
case 12: if (b) {st->r = a/b; return 0;} return 1;
}
return 1;
}
static const char *parseop(struct st *st, const char *s)
{
static const char opch[11] = "|&=!><+-*%/";
static const char opch2[6] = "|&====";
int i;
for (i=0; i<11; i++)
if (*s == opch[i]) {
/* note: >,< are accepted with or without = */
if (i<6 && s[1] == opch2[i]) {
st->op = i;
return s+2;
}
if (i>=4) {
st->op = i+2;
return s+1;
}
break;
}
st->op = 13;
return s;
}
static const char *evalbinop(struct st *st, const char *s, int minprec, int d)
{
static const char prec[14] = {1,2,3,3,4,4,4,4,5,5,6,6,6,0};
unsigned long left;
int op;
d--;
s = evalprim(st, s, d);
s = parseop(st, s);
for (;;) {
/*
st->r (left hand side value) and st->op are now set,
get the right hand side or back out if op has low prec,
if op was missing then prec[op]==0
*/
op = st->op;
if (prec[op] <= minprec)
return s;
left = st->r;
s = evalbinop(st, s, prec[op], d);
if (binop(st, op, left))
return "";
}
}
static const char *evalexpr(struct st *st, const char *s, int d)
{
unsigned long a, b;
if (--d < 0)
return "";
s = evalbinop(st, s, 0, d);
if (*s != '?')
return s;
a = st->r;
s = evalexpr(st, s+1, d);
if (*s != ':')
return "";
b = st->r;
s = evalexpr(st, s+1, d);
st->r = a ? b : st->r;
return s;
}
unsigned long __pleval(const char *s, unsigned long n)
{
struct st st;
st.n = n;
s = evalexpr(&st, s, 100);
return *s == ';' ? st.r : -1;
}
|
