import assert from 'node:assert/strict';
function alu(a, b, op) {
  if (op === 0) {
    const wide = a + b;
    return { y: wide & 255, flag: Number(wide > 255) };
  }
  if (op === 1) return { y: (a - b) & 255, flag: Number(a < b) };
  if (op === 2) return { y: a & b, flag: 0 };
  if (op === 3) return { y: a ^ b, flag: 0 };
  throw new RangeError('operation');
}
assert.deepEqual(alu(250, 10, 0), { y: 4, flag: 1 });
assert.deepEqual(alu(3, 5, 1), { y: 254, flag: 1 });
assert.deepEqual(alu(170, 204, 2), { y: 136, flag: 0 });
assert.deepEqual(alu(170, 204, 3), { y: 102, flag: 0 });
let checks = 0;
for (let a = 0; a < 256; a++) {
  for (let b = 0; b < 256; b++) {
    const add = alu(a, b, 0), sub = alu(a, b, 1);
    assert.equal(add.y + 256 * add.flag, a + b);
    assert.equal(sub.y - 256 * sub.flag, a - b);
    assert.equal(alu(a, b, 2).y | alu(a, b, 3).y, a | b);
    checks += 3;
  }
}
console.log(`ALU PASS: ${checks} identities`);