Integer division without using the / or * operator

Question

I am going through an algorithms and datastructures textbook and came accross this question:

1-28. Write a function to perform integer division withou

Answer 1

unsigned bitdiv (unsigned a, unsigned d)
{
unsigned res,c;

for (c=d; c <= a; c <<=1) {;}

for (res=0;(c>>=1) >= d; ) {
        res <<= 1;
        if ( a >= c) { res++; a -= c; }
        }
return res;
}