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
|
/*************************************************************************
** Calculator.cpp **
** **
** This file is part of dvisvgm -- the DVI to SVG converter **
** Copyright (C) 2005-2010 Martin Gieseking <martin.gieseking@uos.de> **
** **
** This program 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 of **
** the License, or (at your option) any later version. **
** **
** This program 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 this program; if not, see <http://www.gnu.org/licenses/>. **
*************************************************************************/
#include <cmath>
#include <sstream>
#include "Calculator.h"
using namespace std;
// token types
const char END = 0;
const char NUMBER = 1;
const char NAME = 2;
#include <iostream>
/** Evaluates a given arithmetic expression and returns its value.
* The evaluator is implemented as a recursive descendent parser.
* @param[in] is reads expression from this stream
* @return expression value */
double Calculator::eval (istream &is) {
double ret = expr(is, false);
if (lookAhead(is) > 0)
throw CalculatorException("expression syntax error");
return ret;
}
/** Evaluates a given arithmetic expression and returns its value.
* @param[in] expr expression to evaluate
* @return expression value */
double Calculator::eval (const string &expr) {
istringstream iss;
iss.str(expr);
return eval(iss);
}
/** Evaluates the root rule of the expression grammar. */
double Calculator::expr (istream &is, bool skip) { // expr:
double left = term(is, skip);
while (1)
switch (lookAhead(is)) {
case '+': left += term(is, true); break; // term '+' term => $1 + $3
case '-': left -= term(is, true); break; // term '-' term => $1 - $3
default : return left; // term => $1
}
}
double Calculator::term (istream &is, bool skip) { // term:
double left = prim(is, skip);
while (1)
switch (lookAhead(is)) {
case '*': left *= prim(is, true); break; // prim '*' prim => $1 * $3
case '/': { // prim '/' prim => $1 / $3
double denom = prim(is, true);
if (denom == 0)
throw CalculatorException("division by zero");
left /= denom;
break;
}
case '%': { // prim '%' prim => $1 mod $3
double denom = prim(is, true);
if (denom == 0)
throw CalculatorException("division by zero");
left -= denom*floor(left/denom);
break;
}
default: // prim => $1
return left;
}
}
double Calculator::prim (istream &is, bool skip) { // prim:
if (skip)
lex(is);
switch (lookAhead(is)) {
case NUMBER: { // NUMBER => $1
lex(is);
double ret = numValue;
if (lookAhead(is) == NAME) { // NUMBER NAME => $1 * $2
lex(is);
ret *= getVariable(strValue);
}
return ret;
}
case NAME: { // NAME => getVariable($1)
lex(is);
return getVariable(strValue);
}
case '-': // '-' prim => -$2
return -prim(is, true);
case '(': { // '(' expr ')' => $2
double e = expr(is, true);
if (lookAhead(is) != ')')
throw CalculatorException("')' expected");
lex(is);
return e;
}
default:
throw CalculatorException("primary expression expected");
}
}
/** Determines type of next token without swallowing it. That means
* the same token will be read again next time. */
char Calculator::lookAhead (istream &is) {
while (isspace(is.peek())) // skip whitespace
is.get();
if (is.eof())
return END;
int c = is.peek();
if (isdigit(c) || c == '.')
return NUMBER;
if (isalpha(c))
return NAME;
return char(c);
}
/** Reads next token and returns its type. The token value is either assigned
* to the object members numValue or strValue depending on the type. The token
* type is represented by a unique integer. In contrast to method 'lookAhead'
* lex consumes the read token.
* @param[in] is next token is read from this stream
* @return token type */
char Calculator::lex (istream &is) {
int tokenType = lookAhead(is);
switch (tokenType) {
case NUMBER:
is >> numValue;
break;
case NAME: {
strValue.clear();
while (isalpha(is.peek()))
strValue += char(is.get());
break;
}
default:
tokenType = is.get();
}
return char(tokenType);
}
/** Returns the value of a previously defined variable. If there
* is no variable of the given name, a CalculatorException is thrown.
* @param[in] name name of variable
* @return assigned value */
double Calculator::getVariable (const string &name) const {
map<string,double>::const_iterator it = variables.find(name);
if (it == variables.end())
throw CalculatorException("undefined variable '" + name + "'");
return it->second;
}
|