Polynomial.hpp

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#pragma once
 
#include "AstGlobal.h"
#include "AstUtil/StringView.hpp"
#include <vector>
#include <string>
 
AST_NAMESPACE_BEGIN
 
class Polynomial;
 
AST_UTIL_API errc_t aParsePolynomial(StringView content, StringView varname, std::vector<double>& coeffs);
 
 
AST_UTIL_API errc_t aParsePolynomial(StringView content, std::vector<double>& coeffs);
 
 
AST_UTIL_API std::string aFormatPolynomial(const std::vector<double>& coeffs, StringView varname);
 
 
class Polynomial
{
public:
    Polynomial() = default;
    Polynomial(const std::initializer_list<double>& init)
        : coeffs_{init}
    {}
    Polynomial(const std::vector<double>& coeff)
        : coeffs_{coeff}
    {}
    ~Polynomial() = default;
    
    errc_t parse(StringView content, StringView varname){
        return aParsePolynomial(content, varname, coeffs_);
    }
    
    errc_t parse(StringView content){
        return aParsePolynomial(content, coeffs_);
    }
 
    std::string toString(StringView varname)
    {
        return aFormatPolynomial(coeffs_, varname);
    }
 
    const std::vector<double>& coeffs() const { return coeffs_; }
    std::vector<double>& coeffs() { return coeffs_; }
    void setCoeffs(const std::vector<double>& coeffs){ coeffs_ = coeffs; }
    void setCoeffs(std::vector<double>&& coeffs){ coeffs_ = std::move(coeffs); }
    
    double eval(double x) const;
protected:
    std::vector<double> coeffs_;
};
 
 
// Horner法则/秦九韶算法计算多项式值
inline double Polynomial::eval(double x) const
{
    if(coeffs_.size() == 0){
        return 0;
    }
    else if(coeffs_.size() == 1)
    {
        return coeffs_[0];
    }
    else{
        // 使用 Horner 法则计算多项式值
        double temp = coeffs_.back();
        for (int i = (int)coeffs_.size() - 2; i >= 0; --i) {
            temp *= x;
            temp += coeffs_[i];
        }
        return temp;
    }
}
 
A_ALWAYS_INLINE errc_t aParsePolynomial(StringView content, Polynomial& poly)
{
    return poly.parse(content);
}
 
A_ALWAYS_INLINE errc_t aParsePolynomial(StringView content, StringView varname, Polynomial& poly)
{
    return poly.parse(content, varname);
}
 
AST_NAMESPACE_END