code: function shift(b, rowBytes) {
    return Buffer.concat([b.slice(-rowBytes), b.slice(0, -rowBytes)], b.length);
  }
docs: const fs = require('fs'); const util = require('util'); const readFile = util.promisify(fs.readFile); /* function timer(t) {
  console.log(`Waiting ${t}`);
  return new Promise((f, r) => {
  setTimeout(f, t);
  });
  }