You are given a new atomic primitive, called FetchAndSubtract(). It executes as a single atomic instruction, and is defined as follows: int FetchAndSubtract(int *location) {
int value = *location; // read the value pointed to by location
*location = value - 1; // decrement it, and store result back
return value; // return old value
}

Write the lock_init(), lock(), and unlock() routines that use FetchAndSubtract() to implement a working lock. Also define a lock_t structure.