# C++ solution, 0ms, don't have to check for sign, has comments.

• ``````class Solution {
public:
int getSum(int a, int b) {
// Take 1 + 2 for example in 4 bits.
// Same as 0001 + 0010
// Binary addition requires going through each bit position and
// generating a carry in bit, carry out bit and sum bit.
// For example, in bit position 0 in 0001 + 0010,
// carry in: 0, sum bit: carry in + 1 + 0 = 1, carry out: 0
// For bit position 1,
// carry in: 0, sum bit: carry in + 0 + 1 = 1, carry out: 0
// Using a truth table, we can figure out that
// sum bit = carry in xor bit_a xor bit_b.
// carry out = (carry in AND bit_a) OR (carry in AND bit_b) OR (bit_a AND bit_b)
// carry out becomes the carry in for the next bit position.
int result = 0x0;
int sum_bit = 0x0;
int carry_bit = 0x0;
int bit_a = 0x0;
int bit_b = 0x0;

int i = 0;  // Keep track of what bit position im in.
// Isolate bits in each bit position.
bit_a = (a & bitmask) >> i;
bit_b = (b & bitmask) >> i;

// Calculate sum, carry_bit is a carry in now.
sum_bit = ((carry_bit ^ bit_a) ^ bit_b);
// Shift sum_bit to correct bit position, OR into result.
result |= (sum_bit << i);
// Calculate carry out, carry_bit is now a carry out after calculation.
carry_bit = ((bit_a & bit_b) | (carry_bit & bit_a)) | (carry_bit & bit_b);

// Shift bitmask over 1 to the left.