Function benchmark

test/utils.ts:361–399

(
  fn: () => void,
  expected?: { time: number; mem: number; exprs: number }
)

  expected?: { time: number; mem: number; exprs: number }
) {
  const startMem = process.memoryUsage().heapUsed;
  const start = globalThis.performance.now();

  fn();

  const end = globalThis.performance.now();
  const endMem = process.memoryUsage().heapUsed;

  const delta = {
    time: end - start,
    mem: endMem - startMem,
  };
  if (!expected) {
    console.log('mem:', delta.mem, ', time:', delta.time.toFixed(2));
    return 1000;
  }

  // Memory is not a reliable measurement because of unpredictable GC
  const variance = delta.time / expected.time - 1;

  if (true || Math.abs(variance) > 0.1) {
    console.error(
      `\u001b[0mVariance ${(variance * 100).toFixed(1)}% (actual vs expected)`,
      `\n     mem ${emoji(delta.mem, expected.mem)}` +
        `${memToString(delta.mem)} (${memToString(expected.mem)} ${Number(
          (100 * delta.mem) / expected.mem
        ).toFixed(2)}%)` +
        `\n    time ${emoji(delta.time, expected.time)}`,
      `${timeToString(delta.time)} (${timeToString(expected.time)} ${Number(
        (100 * delta.time) / expected.time
      ).toFixed(2)}%)`
    );
  }
  return variance;
}

function emoji(a, b): string {
  if (a === b) return '✅';
  if (a < b) return '\u001b[32m\u25BC\u001b[0m'; // green up triangle
  return '\u001b[31m\u25B2\u001b[0m';
}