convertHtoHMS function Null safety

Implementation

void convertHtoHMS(Model m) {
  Value round(Value v, int digits) => FixFloatFormatter(digits).round(v);

  final Value hr = m.x.intOp();
  final int hrDigits = (hr == Value.zero) ? 0 : (hr.exponent + 1);
  if (hrDigits >= 10) {
    m.resultX = m.x;
    return;
  }
  Value min = Value.fromDouble(m.x.fracOp().asDouble * 60);
  int digitsLeft = 10 - hrDigits; // 1..10
  if (hrDigits == 0 && min.intOp() == Value.zero) {
    final sec = round(Value.fromDouble(min.asDouble * 60), 7);
    final secD = sec.asDouble;
    if (secD >= 60.0) {
      m.resultX = Value.fromDouble(0.01);
    } else if (secD <= -60.0) {
      m.resultX = Value.fromDouble(-0.01);
    } else {
      m.resultX = Value.fromDouble(secD).timesTenTo(-4);
    }
    return;
  }
  // >= 1 minute
  if (digitsLeft != 10) {
    min = round(min.timesTenTo(-2), digitsLeft).timesTenTo(2);
  }
  final minD = min.intOp().asDouble;
  if (minD.abs() >= 60.0) {
    // I believe this branch is impossible, but just to be extra paranoid...
    final minSec = "0.5959999999".substring(0, 2 + digitsLeft);
    if (minD > 0) {
      m.resultX = Value.fromDouble(hr.asDouble + double.parse(minSec));
    } else {
      m.resultX = Value.fromDouble(hr.asDouble - double.parse(minSec));
    }
    return;
  }
  digitsLeft -= 2;
  assert(minD <= 59 && minD >= -59);
  if (digitsLeft <= 0) {
    m.resultX = Value.fromDouble(hr.asDouble + min.timesTenTo(-2).asDouble);
    return;
  }
  Value sec = Value.fromDouble(min.fracOp().asDouble * 60);
  if (digitsLeft == 1) {
    final tensSec = round(sec.timesTenTo(-1), 0).asDouble; // tens of seconds
    if (tensSec.abs() >= 6) {
      // I believe this branch is impossible, too.
      if (tensSec > 0) {
        m.resultX = Value.fromDouble(hr.asDouble + minD / 100 + 0.005);
      } else {
        m.resultX = Value.fromDouble(hr.asDouble + minD / 100 - 0.005);
      }
    } else {
      m.resultX = Value.fromDouble(hr.asDouble + minD / 100 + tensSec / 1000);
    }
    return;
  }
  digitsLeft -= 2;
  assert(digitsLeft >= 0);
  final secD = round(sec, digitsLeft).asDouble;
  if (secD.abs() >= 60) {
    // I believe this branch is impossible, but I'm still paranoid.
    final secStr = "0.0059999999".substring(0, 4 + digitsLeft);
    if (secD > 0) {
      m.resultX =
          Value.fromDouble(hr.asDouble + minD / 100 + double.parse(secStr));
    } else {
      m.resultX =
          Value.fromDouble(hr.asDouble + minD / 100 - double.parse(secStr));
    }
  } else {
    m.resultX = Value.fromDouble(hr.asDouble + minD / 100 + secD / 10000);
  }
}