FULL PRODUCT VERSION :
java version "1.6.0_16"
Java(TM) SE Runtime Environment (build 1.6.0_16-b01)
Java HotSpot(TM) Server VM (build 14.2-b01, mixed mode)


ADDITIONAL OS VERSION INFORMATION :
SunOS opteron 5.11 snv_125 i86pc i386 i86pc


A DESCRIPTION OF THE PROBLEM :
It is possible to create BigInteger so large that its bit length larger than Integer.MAX_VALUE. In these case bitLength() method returns negative "int" value and toByteArray() method crashes.

IMHO, the range of possible BigInteger values should be limited either to a range
[-2^Integer.MAX_VALUE,2^Integer.MAX_VALUE-1] with bit length <= Integer.MAX_VALUE
or to a symmetrical range
[-2^Integer.MAX_VALUE+1,2^Integer.MAX_VALUE-1].

STEPS TO FOLLOW TO REPRODUCE THE PROBLEM :
1) Save "Source code for an executable test case" as TestLargeBigInteger.java
2) javac TestLargeBigInteger.java
3) java TestLargeBigInteger

EXPECTED VERSUS ACTUAL BEHAVIOR :
EXPECTED -
I expect ArithmeticExceptionon when the result of shiftLeft() method is out of suggested BigInteger range.
--------------------
Exception in thread "main" java.lang.ArithmeticException: BigInteger overflow
        at java_math.BigInteger.<init>(BigInteger.java:949)
        at java_math.BigInteger.shiftLeft(BigInteger.java:2129)
        at TestLargeBigInteger.main(TestLargeBigInteger.java:6)

ACTUAL -
The bitLength() method returns negative result and toByteArray method throws an exception.
-------------------------
bitLength=-2147483648
java.lang.NegativeArraySizeException
	at java.math.BigInteger.toByteArray(BigInteger.java:2667)
	at TestLargeBigInteger.main(TestLargeBigInteger.java:9)


REPRODUCIBILITY :
This bug can be reproduced always.

---------- BEGIN SOURCE ----------
import java.math.BigInteger;

public class TestLargeBigInteger {
    public static void main(String[] args) {

        BigInteger x = BigInteger.ONE.shiftLeft(Integer.MAX_VALUE); // x = 2^Integer.MAX_VALUE;
        System.out.println("bitLength="+x.bitLength());
        try {
            byte[] bytes = x.toByteArray();
        } catch (Exception e) {
            e.printStackTrace(System.out);
        }
    }
}
---------- END SOURCE ----------

CUSTOMER SUBMITTED WORKAROUND :
I am preparing a fix and a test for this bug:

http://kenai.com/projects/rigorousnum/sources/java_math/content/trunk/java_math/src/java_math/BigInteger.java?rev=17
http://kenai.com/projects/rigorousnum/sources/java_math/content/trunk/BigIntegerTests/src/HugeValues.java?rev=17
http://kenai.com/projects/rigorousnum/sources/java_math/content/trunk/BigIntegerTests/src/ExtremeShiftingTests.java?rev=17

However I'm going to test more before I submit a WebRev.