c function help needed [on hold]

inline int scan_d(void){
    int n=0,s=1;
    char p=get();
    if(p=='-')  s=-1;
    while((p<'0'||p>'9')&&p!=EOF&&p!='-') p=get();
    if(p=='-') s=-1,p=get();
    while(p>='0'&&p<='9') { n = (n<< 3) + (n<< 1) + (p - '0'); p=get(); }
    return n*s;
}

Can someone please help me out with the above function?

Actually I needed some help for my project and came across this function while searching the internet. This has been used in case of scanf that is taking the input from console.

I am not able to understand the logic.