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/*************************************************************************
** Calculator.cpp **
** **
** This file is part of dvisvgm -- a fast DVI to SVG converter **
** Copyright (C) 2005-2019 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 <stdexcept>
#include "Calculator.hpp"
using namespace std;
// token types
const char END = 0;
const char NUMBER = 1;
const char NAME = 2;
/** Evaluates a given arithmetic expression and returns its value.
* The evaluator is implemented as a recursive descent 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);
for (;;) {
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);
for (;;)
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) {
is >> ws;
int c = is.peek();
if (is.eof())
return END;
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: {
string str;
while (isdigit(is.peek()) || is.peek() == '.')
str += char(is.get());
try {
_numValue = stod(str);
}
catch (const exception&) {
throw CalculatorException("invalid number: "+str);
}
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 {
auto it = _variables.find(name);
if (it == _variables.end())
throw CalculatorException("undefined variable '" + name + "'");
return it->second;
}
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