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The Dart SDK, including the VM, JS and Wasm compilers, analysis, core libraries, and more.
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Decide if we want to generate DivisionByZeroException errors #26

Closed DartBot closed 9 years ago

DartBot commented 13 years ago

This issue was originally filed by garysweave...@gmail.com

Dart should not report a number divided by zero as infinity. And if infinity is allowed, math using infinity should be correct.

What steps will reproduce the problem?

  1. Use the following code:

main() {   print(1 / 0);   print((1 / 0) / (1 / 0)); }

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

It should report:

NaN NaN

Instead it reports:

Infinity NaN

What version of the product are you using? On what operating system?

Using the following on Oct 10, 2011 15:50 EDT

http://www.dartlang.org/docs/getting-started/

Please provide any additional information below.

DartBot commented 13 years ago

This comment was originally written by rice@google.com

This is standard IEE 754 behavior: 1/0 = +Infinity, -1/0 = -Infinity, Infinity/Infinity = NaN. Dart isn't doing anything differently here than either Java or JavaScript.

DartBot commented 13 years ago

This comment was originally written by rice@google.com

(IEE ==> IEEE)

DartBot commented 13 years ago

This comment was originally written by garysw...@gmail.com

You mean just Javascript.

Even though the following does produce Infinity and NaN:

<html> <body> <script> alert(1/0); alert((1/0)/(1/0)); </script> </body> </html>

It is invalid in Java, e.g.:

public class Test {   public static void main(String args[]) {     System.out.println( "" + (1/0));     System.out.println( "" + ((1/0)/(1/0)));   } }

results in:

$ java Test Exception in thread "main" java.lang.ArithmeticException: / by zero     at Test.main(Test.java:3)

Still, Dart is a new language. Couldn't it aspire to get math right instead of being just another Javascript?

Thanks!

DartBot commented 13 years ago

This comment was originally written by rice@google.com

Your Java example is dividing ints, not (IEEE 754) floats or doubles. Please replace 1 with 1.0 and 0 with 0.0 and give your code another try.

DartBot commented 13 years ago

This comment was originally written by rice@google.com

IEEE 754 is what hardware implements -- so adopting a different set of semantics for floating-point numbers means relying on software to do the heavy lifting, and puts code at a big disadvantage versus code that is designed to take advantage of what the floating-point hardware can do.

I thing there is a separate issue of how dividing ints should behave in Dart -- note that the / operator produces a num, not an int, even when dividing two ints. For example, 1/2 = 0.5, like JavaScript, not 0 as in Java. There is a ~/ operator that truncates to int. Currently, (1 ~/ 0) also evaluates to Infinity -- this seems like it would be worth taking up with the spec folks.  

DartBot commented 13 years ago

This comment was originally written by garysw...@gmail.com

Yes, for Float and Double, but fails again with BigDecimal:

import java.math.BigDecimal;

public class Test {   public static void main(String args[]) {     System.out.println( "" + (1F/0F));     System.out.println( "" + ((1F/0F)/(1F/0F)));     System.out.println( "" + (1D/0D));     System.out.println( "" + ((1D/0D)/(1D/0D)));     System.out.println( "" + (new BigDecimal(1D).divide(new BigDecimal(0D), BigDecimal.ROUND_UNNECESSARY)));     System.out.println( "" + ((new BigDecimal(1D).divide(new BigDecimal(0D), BigDecimal.ROUND_UNNECESSARY)).divide(new BigDecimal(1D).divide(new BigDecimal(0D), BigDecimal.ROUND_UNNECESSARY), BigDecimal.ROUND_UNNECESSARY)));   } }

Produces:

$ java Test Infinity NaN Infinity NaN Exception in thread "main" java.lang.ArithmeticException: / by zero     at java.math.BigDecimal.divide(BigDecimal.java:1327)     at java.math.BigDecimal.divide(BigDecimal.java:1444)     at Test.main(Test.java:9)

But it looks like Ruby 1.8.7 still does what you are saying even with BigDecimal:

$ irb

1/0 ZeroDivisionError: divided by 0     from (irb):1:in `/'     from (irb):1 1.0/0.0 => Infinity (1.0/0.0)/(1.0/0.0) => NaN require 'bigdecimal' BigDecimal("1.0") / BigDecimal("0.0") => #<BigDecimal:100605f80,'Infinity',4(24)> (BigDecimal("1.0") / BigDecimal("0.0")) / (BigDecimal("1.0") / BigDecimal("0.0")) => #<BigDecimal:1005fbff8,'NaN',4(56)>

Oh, well. It's a shame that we still settle for that. :)

DartBot commented 13 years ago

This comment was originally written by garysw...@gmail.com

You can close this if you want. Sorry to bother about it.

DartBot commented 13 years ago

This comment was originally written by garyswea...@gmail.com

Oops, just saw your other comment. Yes, feel free to take up with the spec folks about ints being treated as floating points. Glad I could be of limited assistance.

floitschG commented 13 years ago

DartC (the compiler from Dart to JavaScript) is not spec-compliant with regards to numbers. We compile dart numbers to JavaScript numbers (thus losing the distinction between ints and doubles). dart: x / 0 throws a DivisionByZeroException in correct Dart. In dart->Js code it unfortunately becomes the equivalent of x / 0.0 which becomes infinity/nan.

DartBot commented 13 years ago

This comment was originally written by drfibonacci@google.com

Added Area-Language, Triaged labels.

gbracha commented 13 years ago

The spec was carefully thought out and it describes the intended semantics of Dart. We make allowances for dartC, and maybe it is unreasonable to do the right thing and still be performant. But AFIK, this isn't a spec issue unless we want to enshrine special dispensation for dartC in the spec.

Removed Area-Language label. Added Area-Compiler label. Changed the title to: "dartC compiles both ints and doubles into Javascript numbers".

DartBot commented 13 years ago

This comment was originally written by Sebastia...@gmail.com

To me, it seems that JS is correct here. 1/0 is infinity. infinity / infinity is undefined, a.k.a. NaN.

DartBot commented 13 years ago

This comment was originally written by mmendez@google.com

As Florian said, the original target for the java-based dartc was to compile dart numbers to JS numbers.

The only thing that we can do here is to decide whether it is worth checking for division by zero in the current dartc or not -- I changed the description accordingly.

Changed the title to: "dartc does not generate DivisionByZeroException errors".

DartBot commented 12 years ago

This comment was originally written by zundel@google.com

Unassigned from area=compiler. This bug is no longer valid for dartc, but I believe is still a general dart to Javsscript translation issue. If not, please close.

Removed Area-Compiler label. Added New label.

anders-sandholm commented 12 years ago

Added Area-Dart2JS, Triaged labels.

kasperl commented 12 years ago

Changed the title to: "Make sure dart2js generates DivisionByZeroException errors".

kasperl commented 12 years ago

Update summary to reflect that we haven't decided yet.

Changed the title to: "Decide if we want to generate DivisionByZeroException errors".

kasperl commented 12 years ago

Added this to the Later milestone.

kasperl commented 12 years ago

Removed this from the Later milestone.