2adderSubtraction.js

// Two-bit adder/subtractor (manual chaining of two full adders)
let a = [1, 1];          
let b = [1, 1];          
let sub = 0;             // control: 1 for subtraction, 0 for addition

// For subtraction, we invert b and set initial carry to 1
let carry = sub ? 1 : 0; 
let result = [];

// Invert b bit if sub == 1 using xor (acts as a controlled inverter)
let b0 = b[1] ^ sub;
let sumLSB = a[1] ^ b0 ^ carry;
let carryOut = (a[1] & b0) | (b0 & carry) | (a[1] & carry);
result[1] = sumLSB;
carry = carryOut;

let b1 = b[0] ^ sub;
let sumMSB = a[0] ^ b1 ^ carry;
let carryOut2 = (a[0] & b1) | (b1 & carry) | (a[0] & carry);
result[0] = sumMSB;
carry = carryOut2;


if (carry === 1) { 
    result.unshift(1);
}

// Display the result
console.log('  a:', a);
console.log('  b:', b);
console.log('  sub:', sub);
console.log('------------');
console.log('result:', result);