luhnValid function

bool luhnValid(
  1. String digits
)

Whether the digit string passes the Luhn checksum.

Implementation

bool luhnValid(String digits) {
  var sum = 0;
  var doubled = false;
  for (var i = digits.length - 1; i >= 0; i--) {
    var d = digits.codeUnitAt(i) - 48;
    if (doubled) {
      d *= 2;
      if (d > 9) d -= 9;
    }
    sum += d;
    doubled = !doubled;
  }
  return sum % 10 == 0;
}