what is fastio used for in c++ code example

Example: fastinput c++

void fastInput(int &x)
    {
        bool neg=false;
        register int c;
        x =0;
        c=getchar();
        if(c=='-')
        {
            neg = true;
            c=getchar();
        }
        for(;(c>47 && c<58);c=getchar())
          	//bit shifting is faster than other operation
          	//here code below is same as 
          	//x = x*10 + c-48
          
            x = (x<<1) + (x<<3) +c -48;
        if(neg)
            x *=-1;
    }