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  1. JDK
  2. JDK-8141407

Wrong evaluation of a != a when a = NaN

    Details

    • Subcomponent:
    • Introduced In Version:
    • Resolved In Build:
      b96
    • CPU:
      generic
    • OS:
      generic

      Description

      FULL PRODUCT VERSION :
      java version "1.8.0_66"
      Java(TM) SE Runtime Environment (build 1.8.0_66-b17)
      Java HotSpot(TM) 64-Bit Server VM (build 25.66-b17, mixed mode)

      javac 1.8.0_66


      ADDITIONAL OS VERSION INFORMATION :
      Linux 3.2.0-29-generic #46-Ubuntu SMP Fri Jul 27 17:03:23 UTC 2012 x86_64 x86_64 x86_64 GNU/Linux

      EXTRA RELEVANT SYSTEM CONFIGURATION :
      Running with Eclipse Mars.

      A DESCRIPTION OF THE PROBLEM :
      According to specifications NaN should be different from every number, including itself, i.e. NaN != NaN should return true. If a != a is evaluated with Nashorn Javascript, it produces false, even if a == NaN. In fact the first evaluation returns true, but a second identical evaluation with the same ScriptEngine returns false.


      REGRESSION. Last worked in version 7u80

      ADDITIONAL REGRESSION INFORMATION:
      java version "1.8.0_31"
      java-7-openjdk-amd64

      We could check that the results were still correct with the two above versions (though not with an identical programme), but these are no longer installed on our computers.


      STEPS TO FOLLOW TO REPRODUCE THE PROBLEM :
      Execute the programme in "Source code for an executable test case:"

      EXPECTED VERSUS ACTUAL BEHAVIOR :
      EXPECTED -
      true
      true
      true
      true
      true
      ACTUAL -
      true
      false
      false
      true
      true


      REPRODUCIBILITY :
      This bug can be reproduced always.

      ---------- BEGIN SOURCE ----------
      package test;

      import javax.script.ScriptEngine;
      import javax.script.ScriptEngineManager;
      import javax.script.ScriptException;

      public class DummyClass21d {
          static ScriptEngineManager mgr = new ScriptEngineManager();

          public static void main(String[] args) throws ScriptException {
              ScriptEngine engine = mgr.getEngineByName("JavaScript");
              // Compute twice the same. Do we get the same result ?
              engine.eval("a1 = NaN; outCome = (a1!=a1);");
              System.out.println(engine.get("outCome").toString());
              engine.eval("a1 = NaN; outCome = (a1!=a1);");
              System.out.println(engine.get("outCome").toString());
              engine.eval("a1 = NaN; outCome2 = (a1!=a1);");
              System.out.println(engine.get("outCome2").toString());
              engine.eval("a1 = NaN; a2 = NaN; outCome = (a1!=a2);");
              System.out.println(engine.get("outCome").toString());
              engine.eval("a1 = NaN; outCome = (isNaN(a1));");
              System.out.println(engine.get("outCome").toString());
          }
      }

      ---------- END SOURCE ----------

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            • Assignee:
              hannesw Hannes Wallnoefer
              Reporter:
              webbuggrp Webbug Group
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              Dates

              • Created:
                Updated:
                Resolved: