// Factor = (UnaryOp Factor) | (PowerBase ['^' Factor])
Rpn::CodeThread Parser::factor()
{
Rpn::CodeThread result;
// UnaryOp Factor
if (CheckLexeme::isUnaryOperation(m_lexer->lexeme())) {
LexemeType lexemeType = m_lexer->lexeme().type;
m_lexer->nextLexeme();
if (lexemeType == LexemeMinus) {
result = m_codeGenerator->generateUnaryMinus(factor());
}
else if (lexemeType == LexemePlus) {
result = factor();
}
else {
THROW(EInternal());
}
}
// PowerBase ['^' Factor]
else {
result = powerBase();
// ['^' Factor]
if (m_lexer->lexeme().type == LexemePower) {
m_lexer->nextLexeme();
result = m_codeGenerator->generateBinaryOperation(BinaryOperationPower, result, factor());
}
}
return result;
}
{
return base * base;
}
// 递归处理
if (exponent % 2 == 1)
{
return power(power(base, exponent >> 1), 2) * base;
}
else
{
return power(power(base, exponent >> 1), 2);
}
}
double result = powerBase(base, exponent);
if (isPositive)
{
return result;
}
return 1 / result;
}
/****************** 参考答案 ********/
bool g_InvalidInput = false;
double power(double base, int exponent)
{
g_InvalidInput = false;
