UTC_serializer_parser.js

// Efficient functions that serialize to and parse from this format: 
// "YYYY-MM-DD HH:mm:ss"

function formatUTC(date) {
  const y = date.getUTCFullYear();
  const m = date.getUTCMonth() + 1;
  const d = date.getUTCDate();
  const H = date.getUTCHours();
  const M = date.getUTCMinutes();
  const S = date.getUTCSeconds();

  return (
    y + "-" +
    (m < 10 ? "0" : "") + m + "-" +
    (d < 10 ? "0" : "") + d + " " +
    (H < 10 ? "0" : "") + H + ":" +
    (M < 10 ? "0" : "") + M + ":" +
    (S < 10 ? "0" : "") + S
  );
}

// Read 2 and 4 digits without creating substrings
const d2 = (i,s) => (s.charCodeAt(i) - 48) * 10 + (s.charCodeAt(i + 1) - 48);
const d4 = (i,s) =>
    (s.charCodeAt(i) - 48) * 1000 +
    (s.charCodeAt(i + 1) - 48) * 100 +
    (s.charCodeAt(i + 2) - 48) * 10 +
     s.charCodeAt(i + 3) - 48;

// assumes exact format "YYYY-MM-DD HH:mm:ss"
function parseUTC_yyyyMMdd_HHmmss(s) {
  // Quick delimiter checks (cheap, helps avoid misparsing)
  if (s.length !== 19 ||
      s.charCodeAt(4) !== 45 || // -
      s.charCodeAt(7) !== 45 || // -
      s.charCodeAt(10) !== 32 || // space
      s.charCodeAt(13) !== 58 || // :
      s.charCodeAt(16) !== 58)   // :
    return null; // or throw

  const year  = d4(0,s);
  const month = d2(5,s);   // 1–12
  const day   = d2(8,s);   // 1–31 (rough check optional)
  const hour  = d2(11,s);  // 0–23
  const min   = d2(14,s);  // 0–59
  const sec   = d2(17,s);  // 0–59

  // Optional light range checks (skip if you want every last ns)
  if (month < 1 || month > 12 || day < 1 || day > 31 ||
      hour > 23 || min > 59 || sec > 59) return null;

  // Construct as UTC
  return new Date(Date.UTC(year, month - 1, day, hour, min, sec));
}