Dart double "bitwise not" is giving different result (~~-1 != -1)-CodePudding

so I am running dart on DartPad And I tried running the following code:

import 'dart:math';

void main() {
  print(~0);
  print(~-1);
  print(~~-1);
}

Which resulted in the following outputs

4294967295
0
4294967295

As you can see inverting the bits from 0 results in the max number (I was expecting -1 as dart uses two's complement) and inverting from -1 results in 0, which creates the situation where inverting 2 times -1 does not give me -1.

Looks like it's ignoring the first bit when inverting 0, why is that?

CodePudding user response：

Dart compiled for the web (which includes DartPad) uses JavaScript numbers and number operations. One of the consequences of that is that bitwise operations (~, &, |, ^, <<, >> and >>> on int) only gives 32-bit results, because that's what the corresponding JavaScript operations do.

For historical reasons, Dart chooses to give unsigned 32-bit results, not two's complement numbers. So ~-1 is 0 and ~0 is the unsigned 0xFFFFFFFF, not -1.

In short, that's just how it is.