Shift right operator with signed values gives inconsistent results.

[DartBot]

This issue was originally filed by @bp74

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What steps will reproduce the problem?

1. Try this code:

  int color = 0xA0FFFFFF;
  int alpha1 = (color >> 24) & 0xFF;
  int alpha2 = (color & 0xFF000000) >> 24;
  print("$alpha1 / $alpha2");

What is the expected output? What do you see instead?

Dart says: "160 / 160"
When you compile it to JS, it says: "160 / -96"

It should not be different of course, maybe Dart need to support the ">>>" operator like JS does (https://developer.mozilla.org/en/JavaScript/Reference/Operators/Bitwise_Operators).

Or the frog compiler has to compile the Dart ">>" to a JS ">>>". Which i think is the right solution, because the default behaviour of JS is very strange and should not be replicated in Dart.

What version of the product are you using? On what operating system?
Dart Editor 7364 32 bit, Windows 7 64 bit

[ghost]

Dart integers do not have a fixed range, therefore a logical shift right on integers makes no sense. What you maybe want is a logical shift right on 32-bit/64-bit values.

The behavior that you observe above is incorrect and may have been fixed in the meantime. In Dart a shift left/right preserves the sign of the shifted value.

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cc @floitschG.

[floitschG]

Currently we compile all Dart numbers to JavaScript numbers. That means that we cannot support the correct spec there.
However, as you mention: having negative numbers as result of bit-operations is usually not what you want. In the dart2js (which will replace the current dart-to-javascript compiler) this has been recently fixed (by using ">>>"). There all bit-operations return positive results.
Closing as duplicate of the same bug for dart2js.

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Added Duplicate label.
Marked as being merged into #2725.