//$Id: bignum.h,v 1.2 2006-09-26 19:05:32 cactus Exp $ -*- c++ -*-

#ifndef EAF_BIGNUM_H
#define EAF_BIGNUM_H

#include <string>
#include <iostream>

class Bignum
{
    typedef unsigned char digit_t;
    
    size_t   n;
    digit_t *d;
    
public:
    Bignum ();
    explicit Bignum (const std::string &s);
    
    ~Bignum ();

    Bignum (const Bignum &that);
    Bignum& operator= (const Bignum &that);

    std::string str () const;

    friend bool operator== (const Bignum &x, const Bignum &y);
    friend bool operator<  (const Bignum &x, const Bignum &y);
    
    friend Bignum operator+ (const Bignum &x, const Bignum &y);
    friend Bignum operator* (const Bignum &x, const Bignum &y);
    
    Bignum operator+= (const Bignum &y);
    Bignum operator*= (const Bignum &y);
private:
    explicit Bignum (size_t n);    

    digit_t digit_from_char (char c);
    
    static digit_t truncate_digit (digit_t a_plus_b, digit_t &overflow);
};

       bool operator== (const Bignum &x, const Bignum &y);
inline bool operator!= (const Bignum &x, const Bignum &y) { return !(x == y); }

       bool operator<  (const Bignum &x, const Bignum &y);
inline bool operator>  (const Bignum &x, const Bignum &y) { return y < x; }
inline bool operator<= (const Bignum &x, const Bignum &y) { return !(x > y); }
inline bool operator>= (const Bignum &x, const Bignum &y) { return !(x < y); }

Bignum operator+ (const Bignum &x, const Bignum &y);
Bignum operator* (const Bignum &x, const Bignum &y);

std::ostream& operator<< (std::ostream &ostr, const Bignum &bignum);
std::istream& operator>> (std::istream &ostr, Bignum &bignum);

#endif /* EAF_BIGNUM_H */