Is returning a value != '0' or '1' as jboolean from a JNI function legal?

[Jason Greene]

> On Aug 20, 2018, at 12:23 PM, Andrew Haley <aph at redhat.com> wrote:
> 
> On 08/20/2018 04:14 PM, Jason Greene wrote:
> 
>> IMO departing from C semantics (non-zero = TRUE, zero = false)
>> offers little gain and will likely just lead to hard to catch
>> bugs. Even if the JNI developer knows the rules, it will be quite
>> easy for surprises to show up. For example, a developer might assume
>> a library call always returns 1, and wire it straight to a
>> boolean. If this assumption is broken (a condition not taken into
>> account, or future behavioral differences), then it could quickly
>> turn into a lot of wasted time and effort.
> 
> It's tricky, though: a C implementation could silently truncate a
> value of 0xff00_0000 to (jboolean) 0x00, and there's not a damn thing
> that a JVM can do about it: there's literally no way to know.  It's
> pretty much unfixable from our end.

OK but in that case the C developer can see its an unsigned char, and their
compiler is likely to throw an overflow warning. Granted, it’s also true that 
int is a more common return value than unsigned char.

-Jason