I wrote some dart code follow js code and there is a problem , hope someone can help me/
js code:
var max = 0x80000000;
var data = -2000;
var mod = data % max;
the mod value is -2000
Dart code :
var max = 0x80000000;
var data = -2000;
var mod = data % max;
the mod value is 2147481648
Why?
Because JavaScript and Dart are different languages with different operator specifications.
Dart specifies that the remainder operation result is always positive:
https://api.dart.dev/stable/2.10.4/dart-core/num/operator_modulo.html
In JavaScript the remainder can be negative, the sign of the result equals the sign of the dividend:
https://www.ecma-international.org/ecma-262/11.0/index.html#sec-numeric-types-number-remainder
Dart has two "modulo" operators on integers, % (aka. modulo) and remainder.
They differ for negative operands in whether the result takes the sign of the dividend or the divisor. For positive operands the two agree.
Compare:
void main() {
for (var a in [5, -5]) {
for (var b in [3, -3]) {
print("$a ~/ $b = ${a ~/ b}");
print("$a % $b = ${a % b}");
print("$a.remainder($b) = ${a.remainder(b)}");
print("$a = $b * ($a ~/ $b) + $a.remainder($b) = ${b * (a ~/ b) + a.remainder(b)}");
}
}
}
This code shows all the combinations and that a == (a ~/ b) * b + a.remainder(b) in general.