/*  dpow10.cpp by K.Tsuru  */ 
/************************************
 It returns 10^n.
 It asumes that |n| has order of 10.
************************************/
double dpow10(const int n){
    if(!n) return 1.0;
    double r(1), z(10.0);
    int m = n>0 ? n : -n;

    while(1){
        if( m & 1 ) r *= z;
        m /= 2;
        if( !m ) break;
        z *= z;
    }
    if(n > 0) return r;
    return 1.0/r;
}