Question

/*

logicalShift - shift x to the right by n, using a logical shift

can assume that 0<= n <=31

Examples: logicalShift(0x87654321,4) = 0x08675432

Legal ops: ! ~ & ^ | + << >>

Max ops: 20

Rating: 3    */

int logicalShift(int x, int n) {

return 0;

}

How would I code the logicalShift in C?

I have this, but this isn't right. I think I'm in the right track though:

int logicalShift(int x, int n) {

int a = ~0;

int shift = 31 + ((~n)+1);

a=a<<shift;

a=~a;

x=x>>n;

return x & a;

}

Answer 1

int right_logical_shift(int num, int n){
int size_int = 8 * sizeof(int); // Calculating size of int in bits so as to create a bit mask for getting sign bit
int mask = 1<<(size_int - 1); // Creating a mask of the form 0x80000000 (32 bit int)
int sign_bit = (mask&num) == 0?0:1; // Sign bit = 0 if positive number else sign bit = 1
int num_without_sign = num&(~mask); // Removing sign bit from the number ~mask = 0x7FFFFFFF (32 bit int)
num_without_sign>>=n; // Right shift number without sign by n bits
sign_bit <<=(size_int - 1 - n); // Now left shift sign bit (which is either 0 or 1) by size of int - n - 1
num = (sign_bit|num_without_sign); // Logical And operation of sign bit and number without sign gives the
// number logically shifted by n bits
return num;
}