Q:

Implement greater equal sign in C using only bitwise operations

I know that many basic operations like addition or division can also be implemented in C using only bitwise operators. How can I do the same with the greater than or equal sign (>=)? 
if (x >= 0) {
    ...
}

A:

Simplest solution I can come up with:
#include <limits.h>

if ((x & INT_MAX) == x)    // if (x >= 0)
    ...

If you don't like the == then use XOR to do the equals test:
#include <limits.h>

if ((x & INT_MAX) ^ x)    // if (x < 0)
    ...
else                      // else x >= 0
    ...

