Good eye, `input` should be replaced with `result` when building the subkeys within the loop. Here's a working implementation: function feistel(ctr, lr, ll)

Good eye, `input` should be replaced with `result` when building the subkeys within the loop. Here's a working implementation: function feistel(ctr, lr, ll) { let result = ctr; for (var i = 0; i < 8; i++) { let l = (result / ll)|0; let r = result % ll; let temp = r; // alter round fn's multiplier & increment accordingly. let fn = (r * 16807 + i) % lr; r = (l + fn) % lr; l = temp; result = lr * l + r; } return result; } let rsize = 8; let outputs = new Set(); for(let i = 0; i < rsize * rsize; i++) outputs.add(feistel(i, rsize, rsize)) for(let i = 0; i < rsize * rsize; i++) if (!outputs.has(i)) console.log('failure: ', i);