C++大整数模板

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#define MAXN 9999
#define DLEN 4
class Bignum
{
private:
    int a[10010],len;
public:
    Bignum(){ len=1; memset( a , 0 , sizeof(a) ); }
    Bignum( const int );
    Bignum( const char* );
    Bignum &operator=( const Bignum & );
    Bignum operator+( const Bignum & )const;
    Bignum operator-( const Bignum & )const;
    Bignum operator*( const Bignum & )const;
    Bignum operator/( const int & )const;
    Bignum operator^( const int & )const;
    int operator%( const int & )const;
    bool operator>( const Bignum&T )const;
    bool operator>( const int &t )const;
    void print();
};
Bignum::Bignum( const int b )
{
    int c,d=b;
    len = 0;
    memset ( a , 0 , sizeof(a) );
    while ( d>MAXN )
    {
        c = d-(d/(MAXN+1))*(MAXN+1);
        d = d/(MAXN+1);
        a[len++] = c;
    }
    a[len++] = d;
}
Bignum::Bignum( const char*s )
{
    memset ( a , 0 , sizeof(a) );
    int L = strlen(s);
    len = L/DLEN;
    if ( L%DLEN ) len++;
    int index = 0;
    for( int i=L-1 ; i>=0 ; i-=DLEN )
    {
        int t = 0;
        int k = i-DLEN+1;
        if ( k<0 ) k = 0;
        for ( int j=k ; j<=i ; j++ )
            t = t*10+s[j]-'0';
        a[index++] = t;
    }
}
Bignum & Bignum::operator=( const Bignum &n )
{
    len = n.len;
    memset ( a , 0 , sizeof(a) );
    for ( int i=0 ; i<len ; i++ )
        a[i] = n.a[i];
    return *this;
}
Bignum Bignum::operator+( const Bignum &T )const
{
    Bignum t(*this);
    int big = T.len>len?T.len:len;
    for ( int i=0 ; i<big ; i++ )
    {
        t.a[i] += T.a[i];
        if ( t.a[i]>MAXN )
        {
            t.a[i+1]++;
            t.a[i] -= MAXN+1;
        }
    }
    if ( t.a[big]!=0 )
        t.len = big+1;
    else
        t.len = big;
    return t;
}
Bignum Bignum::operator-( const Bignum &T )const
{
    bool flag;
    Bignum t1,t2;
    if ( *this>T )
    {
        t1 = *this;
        t2 = T;
        flag = 0;
    }
    else
    {
        t1 = T;
        t2 = *this;
        flag = 1;
    }
    int big = t1.len;
    for ( int i=0 ; i<big ; i++ )
    {
        if ( t1.a[i]<t2.a[i] )
        {
            int j = i+1;
            while ( t1.a[j]==0 )
                j++;
            t1.a[j--]--;
            while ( j>i )
                t1.a[j--] += MAXN;
            t1.a[i] += MAXN+1-t2.a[i];
        }
        else
            t1.a[i] -= t2.a[i];
    }
    t1.len = big;
    while ( t1.a[t1.len-1]==0&&t1.len>1 )
        t1.len--;
    if ( flag )
        t1.a[t1.len-1] = 0-t1.a[t1.len-1];
    return t1;
}
Bignum Bignum::operator*( const Bignum&T )const
{
    Bignum ret;
    int i,j,up;
    int temp,temp1;
    for ( i=0 ; i<len ; i++ )
    {
        up = 0;
        for ( j=0 ; j<T.len ; j++ )
        {
            temp = a[i]*T.a[j]+ret.a[i+j]+up;
            if( temp>MAXN )
            {
                temp1 = temp-temp/(MAXN+1)*(MAXN+1);
                up = temp/(MAXN+1);
                ret.a[i+j] = temp1;
            }
            else
            {
                up = 0;
                ret.a[i+j] = temp;
            }
        }
        if ( up!=0 )
            ret.a[i+j] = up;
    }
    ret.len = i+j;
    while ( ret.a[ret.len-1]==0&&ret.len>1 ) ret.len--;
    return ret;
}
Bignum Bignum::operator/( const int &b )const
{
    Bignum ret;
    int down=0;
    for ( int i=len-1 ; i>=0 ; i-- )
    {
        ret.a[i] = (a[i]+down*(MAXN+1))/b;
        down = a[i]+down*(MAXN+1)-ret.a[i]*b;
    }
    ret.len = len;
    while ( ret.a[ret.len-1]==0&&ret.len>1 )
        ret.len--;
    return ret;
}
int Bignum::operator%( const int &b )const
{
    int d = 0;
    for ( int i=len-1 ; i>=0 ; i-- )
        d = ( (1LL*d*(MAXN+1))%b+a[i] )%b;
    return d;
}
Bignum Bignum::operator^( const int &n )const
{
    Bignum t,ret(1);
    if ( n<0 ) exit(-1);
    if ( n==0 ) return 1;
    if ( n==1 ) return *this;
    int m = n,i;
    while ( m>1 )
    {
        t = *this;
        for ( i=1 ; (i<<1)<=m ; i<<=1 )
            t = t*t;
        m -= i;
        ret = ret*t;
        if ( m==1 )
            ret = ret*(*this);
    }
    return ret;
}
bool Bignum::operator>( const Bignum &T )const
{
    int ln;
    if ( len>T.len ) return true;
    else if ( len==T.len )
    {
        ln = len-1;
        while ( a[ln]==T.a[ln]&&ln>=0 )
            ln--;
        if ( ln>=0&&a[ln]>T.a[ln] )
            return true;
        else
            return false;
    }
    else
        return false;
}
bool Bignum::operator>( const int &t )const
{
    Bignum b(t);
    return *this>b;
}
void Bignum::print()
{
    int i;
    printf( "%d" , a[len-1] );
    for ( int i=len-2 ; i>=0 ; i-- )
        printf( "%04d" , a[i] );
    printf( "\n" );
}