In C bits, multiply by 3 and divide by 16

Question

A buddy of mine had these puzzles and this is one that is eluding me. Here is the problem, you are given a number and you want to return that number times 3 and divided by 1

Answer 1

what you can do is first divide by 4 then add 3 times then again devide by 4.

3*x/16=(x/4+x/4+x/4)/4

with this logic the program can be

main()
{
   int x=0xefffffff;
   int y;
   printf("%x",x);
   y=x&(0x80000000);
   y=y>>31;
   x=(y&(~x+1))+(~y&(x));
   x=x>>2;
   x=x&(0x3fffffff);
   x=x+x+x;
   x=x>>2;
   x=x&(0x3fffffff);
    x=(y&(~x+1))+(~y&(x));
   printf("\n%x %d",x,x);
}

AND with 0x3fffffff to make msb's zero. it'l even convert numbers to positive. This uses 2's complement of negative numbers. with direct methods to divide there will be loss of bit accuracy for negative numbers. so use this work arround of converting -ve to +ve number then perform division operations.