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  1. JDK
  2. JDK-4713247

REGRESSION: Math error with HotSpot 1.4.1-beta

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    • Subcomponent:
    • Resolved In Build:
      rc
    • CPU:
      x86
    • OS:
      windows_xp

      Description



      Name: rmT116609 Date: 07/11/2002


      FULL PRODUCT VERSION :
      java version "1.4.1-beta"
      Java(TM) 2 Runtime Environment, Standard Edition (build 1.4.1-beta-b14)
      Java HotSpot(TM) Client VM (build 1.4.1-beta-b14, mixed mode)

      FULL OPERATING SYSTEM VERSION :
      Microsoft Windows XP [Version 5.1.2600], Windows 2000

      ADDITIONAL OPERATING SYSTEMS :
      Linux (RedHat 7.3) (#1 Thu Apr 18 07:31:07 EDT 2002)

      A DESCRIPTION OF THE PROBLEM :
      On HotSpot 1.4.1beta with AMD processors, a math error occurs when multipling and adding longs in a certain order.

      It will provide the correct results for a while, but will later begin to give incorrect results. I assume this is an HotSpot optimization that doesn't work correctly.

      REGRESSION. Last worked in version 1.4

      STEPS TO FOLLOW TO REPRODUCE THE PROBLEM :
      1. Run the source code below on an AMD machine (tested on Athlon, K6-2)

      EXPECTED VERSUS ACTUAL BEHAVIOR :
      When running the example source code:

      Expected: Should print this continuously:
      should be 0: 0

      Actual: It prints the above for a few seconds, then prints this:
      should be 0: 8589934592

      The problem is not reproducible if -Xint is used.

      The problem is also reproducible on Windows 2000(Service Pack 2, pentium III processor) using JDK1.4.1-beta.

      ---------- BEGIN SOURCE ----------
      public class MathTest {

          public static void main(String[] args) {
              MathTest test = new MathTest();
              while (true) {
                  // y must be negative, x can be anything
                  long x = -Math.round(Math.random() * 65535L);
                  long y = x;
                  test.compute(x, y);
              }
          }
          
          long a = 1;
          long b = -1;
          
          public void compute(long x, long y) {
             // if the next line is commented out, the problem does not occur
             long answer1 = a * x - b * y;
             long answer2 = a * y + b * x;
             System.out.println("should be 0: " + answer2);
          }
      }


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

      Release Regression From : 1.4.0_01
      The above release value was the last known release where this
      bug was known to work. Since then there has been a regression.

      (Review ID: 159216)
      ======================================================================

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            Assignee:
            never Tom Rodriguez
            Reporter:
            rmandalasunw Ranjith Mandala (Inactive)
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