Duff's device in JavaScript — benchmark from lazutkin.com. Run: npm install && npm run bench

bench-duff.mjs

const SIZE = 127;

export const source = new Array(SIZE);
export const target = new Array(source.length);

for (let i = 0; i < source.length; ++i) {
  source[i] = i;
}

export default {
  'simple-loop': n => {
    for (let i = 0; i < n; ++i) {
      for (let j = 0; j < source.length; ++j) {
        target[j] = source[j];
      }
    }
  },
  'unrolled-loop': n => {
    for (let i = 0; i < n; ++i) {
      let j = 0;
      for (; j + 10 <= source.length; j += 10) {
        target[j] = source[j];
        target[j + 1] = source[j + 1];
        target[j + 2] = source[j + 2];
        target[j + 3] = source[j + 3];
        target[j + 4] = source[j + 4];
        target[j + 5] = source[j + 5];
        target[j + 6] = source[j + 6];
        target[j + 7] = source[j + 7];
        target[j + 8] = source[j + 8];
        target[j + 9] = source[j + 9];
      }
      for (; j < source.length; ++j) {
        target[j] = source[j];
      }
    }
  },
  'duff-device': n => {
    for (let i = 0; i < n; ++i) {
      let j = 0;
      for (; j + 10 <= source.length; j += 10) {
        target[j] = source[j];
        target[j + 1] = source[j + 1];
        target[j + 2] = source[j + 2];
        target[j + 3] = source[j + 3];
        target[j + 4] = source[j + 4];
        target[j + 5] = source[j + 5];
        target[j + 6] = source[j + 6];
        target[j + 7] = source[j + 7];
        target[j + 8] = source[j + 8];
        target[j + 9] = source[j + 9];
      }
      switch (source.length - j) {
        case 9: target[j + 8] = source[j + 8];
        case 8: target[j + 7] = source[j + 7];
        case 7: target[j + 6] = source[j + 6];
        case 6: target[j + 5] = source[j + 5];
        case 5: target[j + 4] = source[j + 4];
        case 4: target[j + 3] = source[j + 3];
        case 3: target[j + 2] = source[j + 2];
        case 2: target[j + 1] = source[j + 1];
        case 1: target[j] = source[j];
      }
    }
  },
  'duff-device-nested': n => {
    for (let i = 0; i < n; ++i) {
      for (let j = 0; j < source.length; j += 10) {
        switch (Math.min(source.length - j, 10)) {
          case 10: target[j + 9] = source[j + 9];
          case 9: target[j + 8] = source[j + 8];
          case 8: target[j + 7] = source[j + 7];
          case 7: target[j + 6] = source[j + 6];
          case 6: target[j + 5] = source[j + 5];
          case 5: target[j + 4] = source[j + 4];
          case 4: target[j + 3] = source[j + 3];
          case 3: target[j + 2] = source[j + 2];
          case 2: target[j + 1] = source[j + 1];
          case 1: target[j] = source[j];
        }
      }
    }
  }
};

package.json

{
  "name": "duff-device-bench",
  "private": true,
  "type": "module",
  "scripts": {
    "bench": "nano-bench bench-duff.mjs"
  },
  "devDependencies": {
    "nano-benchmark": "^1.2.0"
  }
}