RFR:JDK-8190391:nashorn: "!!" of nonzero even integer var becomes false when returned

[Sundararajan Athijegannathan]

Experimented with jasm 
(https://wiki.openjdk.java.net/display/CodeTools/asmtools):

super public class HelloWorld
         version 50:0
{
public Method  "<init>":"()V"
         stack 1 locals 1
{
                 aload_0;
                 invokespecial   Method java/lang/Object."<init>":"()V";
                 return;
}

public static Method func:"(I)Z"
         stack 1 locals 1
{
     iload 0;
     ireturn;
}

public static Method main:"([Ljava/lang/String;)V"
         stack 2 locals 1
{
                 getstatic       Field 
java/lang/System.out:"Ljava/io/PrintStream;";
                 bipush 0;
                 invokestatic    Method HelloWorld.func:"(I)Z";
                 invokevirtual   Method java/io/PrintStream.println:"(Z)V";

                 getstatic       Field 
java/lang/System.out:"Ljava/io/PrintStream;";
                 bipush 13;
                 invokestatic    Method HelloWorld.func:"(I)Z";
                 invokevirtual   Method java/io/PrintStream.println:"(Z)V";

                 getstatic       Field 
java/lang/System.out:"Ljava/io/PrintStream;";
                 bipush 22;
                 invokestatic    Method HelloWorld.func:"(I)Z";
                 invokevirtual   Method java/io/PrintStream.println:"(Z)V";

                 return;
}

} // end Class HelloWorld

prints false, true, false.

-Sundar


On 13/11/17, 1:42 PM, Sundararajan Athijegannathan wrote:
> +1
>
> Yep. 0 and 1 are only allowed.
>
> -Sundar
>
> On 13/11/17, 1:27 PM, Attila Szegedi wrote:
>> +1. Nice catch. Feels like an implementation detail, but the JVM
>> specification is indeed unclear on the behavior in case there's a 
>> bytecode
>> method doing this:
>>
>> public static func(I)Z
>>      0     iload 0
>>      1     ireturn
>>
>>
>> I went spelunking in the JVM spec, and the closest I could find is in
>> section 2.3.4 says "The Java Virtual Machine encodes boolean array
>> components using 1 to represent true and 0 to represent false. Where 
>> Java
>> programming language boolean values are mapped by compilers to values of
>> Java Virtual Machine type int, the compilers must use the same 
>> encoding."
>> So I guess we better stick to that.
>>
>> Attila.
>>
>>
>> On Mon, Nov 13, 2017 at 7:21 AM, Priya Lakshmi Muthuswamy<
>> priya.lakshmi.muthuswamy at oracle.com>  wrote:
>>
>>> Hi,
>>>
>>> Please review JDK-8190391 : nashorn: "!!" of nonzero even integer var
>>> becomes false when returned
>>>
>>> JBS : https://bugs.openjdk.java.net/browse/JDK-8190391
>>> webrev : http://cr.openjdk.java.net/~pmuthuswamy/8190391/webrev.00/
>>>
>>> Thanks,
>>> Priya
>>>