Banker's Rounding in Dart - dart

Question

Can anyone help with a Banker's rounding implementation in Dart please
So i round 3 d.p. to the nearest 2 d.p. number EXCEPT when the number is halfway between it goes to the nearest even number
eg
print(1.011.toStringAsFixed(2)); // rounds down to 1.01
print(1.019.toStringAsFixed(2)); // rounds up to 1.02
print(1.015.toStringAsFixed(2)); // rounds down to 1.01 but i want up to 1.02
print(1.025.toStringAsFixed(2)); // rounds down to 1.02

Answer 1

I have same requirement, so i build one.
banker_rounding.dart
import 'dart:math';
import 'package:decimal/decimal.dart';
Decimal _getDecimalOfNumber(Decimal number, int fractionDigits) => number - (number.floor());
Decimal _pow10(int powNum) => Decimal.parse(pow(10, powNum).toString());
Decimal _carryLatest(Decimal number) {
int decimalLength = number.toString().length - 2;
Decimal offset = _pow10(-decimalLength);
return number + offset;
}
Decimal bankerRound(Decimal value, int fractionDigits) {
// integer of number
Decimal integerOfNumber = value.floor();
// decimal of number
Decimal decimalOfNumber = _getDecimalOfNumber(value, fractionDigits);
// remain flag
int remainFlag = (decimalOfNumber * _pow10(fractionDigits + 1) % Decimal.fromInt(10)).toInt();
Decimal finalMultiple = _pow10(fractionDigits);
Decimal finalDecimalOfNumber = ((decimalOfNumber * finalMultiple).floor() / finalMultiple);
if (remainFlag <= 4) {
// do nothing
} else if (remainFlag >= 6) {
// carry
finalDecimalOfNumber = _carryLatest(finalDecimalOfNumber);
} else {
// check bottom has number
bool hasBottom = _getDecimalOfNumber(decimalOfNumber * _pow10(fractionDigits + 1), fractionDigits) != Decimal.zero;
if (hasBottom) {
// carry
finalDecimalOfNumber = _carryLatest(finalDecimalOfNumber);
} else {
// check pre remain flag
int preLastNumber = (decimalOfNumber * _pow10(fractionDigits) % Decimal.fromInt(10)).toInt();
if (preLastNumber.isOdd) {
// carry
finalDecimalOfNumber = _carryLatest(finalDecimalOfNumber);
} else {
// do nothing
}
}
}
return integerOfNumber + finalDecimalOfNumber;
}

Answer 2

Here is a tested banker round to a whole numbers algorithm.
For Decimal (100% accurate):
import 'dart:math';
import 'package:decimal/decimal.dart';
var _halfDec = Decimal.parse('0.5');
Decimal bankerRoundDecimal(Decimal value) {
var rounded = value.round();
if(rounded - value == _halfDec)
if(value.ceil().toInt() % 2 != 0)
rounded = value.floor();
return rounded;
}
And for double:
double bankerRound(double value) {
var rounded = value.roundToDouble();
if(((rounded - value) * 100).round() == 50)
if(value.ceil() % 2 != 0)
rounded = value.floorToDouble();
return rounded;
}