[Sablevm-bugs] [ sablevm-Bugs-597368 ] Need to workaround the x86 division bug

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Bugs item #597368, was opened at 2002-08-19 16:36
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https://sourceforge.net/tracker/?func=detail&atid=105523&aid=597368&group_id=5523

Category: Execution Problem
Group: SableVM
Status: Open
Resolution: None
Priority: 7
Submitted By: Nobody/Anonymous (nobody)
Assigned to: Etienne M. Gagnon (egagnon)
Summary: Need to workaround the x86 division bug

Initial Comment:
/* test that we don't get tripped up by x86 problem */

public class divtest {

    public static int divfunc(int x, int y) {
      return x/y;
    }

    public static void main(String args[]) {

      int i = 0x80000000;
      int j = -1;

      int k = divfunc(i,j);     // x86 causes trap for
no good reason
      System.out.println("Result is
"+Integer.toHexString(k));
    }
}


This program should output "Result is 80000000" but
instead
we get (when running on i386):

java.lang.ArithmeticException
        at divtest.divfunc(divtest.java:6)
        at divtest.main(divtest.java:14)
        at
java.lang.VirtualMachine.invokeMain(VirtualMachine.java)
        at
java.lang.VirtualMachine.main(VirtualMachine.java:88)

Kaffe ran into this same problem. I don't know the
details but
it has something to do with an x86 integer division
bug.


----------------------------------------------------------------------

Comment By: David Bélanger (davidbelanger)
Date: 2003-01-31 08:21

Message:
Logged In: YES 
user_id=694080


On PPC, that division produces undefined result (on a G3, it
gives -1).  No exception is raised, however it would be
possible to check for overflow (probably would require some
inlined assembly).  We may need some #define in system.c to
handle it for each architecture that produces "incorrect"
result.

FYI, due to the asymmetry of 2's complement, there is no
positive integer equal to 0x80000000 / -1.

David

----------------------------------------------------------------------

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