Array of booleans

[David Lloyd]

On Thu, Mar 18, 2021 at 10:53 AM Maurizio Cimadamore <
maurizio.cimadamore at oracle.com> wrote:

>
> On 18/03/2021 15:43, forax at univ-mlv.fr wrote:
> > ----- Mail original -----
> >> De: "Maurizio Cimadamore" <maurizio.cimadamore at oracle.com>
> >> À: "Remi Forax" <forax at univ-mlv.fr>
> >> Cc: "panama-dev at openjdk.java.net'" <panama-dev at openjdk.java.net>
> >> Envoyé: Jeudi 18 Mars 2021 16:31:12
> >> Objet: Re: Array of booleans
> >> On 18/03/2021 15:28, forax at univ-mlv.fr wrote:
> >>> It works with JNI, boolean is mapped into an unsigned 8 bits
> >>> https://docs.oracle.com/en/java/javase/16/docs/specs/jni/types.html
> >> Yeah - it seems to be a case of different specs pointing to different
> >> decisions :-)
> >>
> >> If the format of booleans is truly unspecified at the JVMS level (which
> >> seems to be the case), then it seems like JNI is taking things a step
> >> too far?
> > I don't think you can practically interact with the C world if you do
> not fully specify the memory layout of all the primitive types of Java,
> hence jboolean being defined as an unsigned byte.
>
> True, but note that this is not a problem we have with the linker; the
> linker supports the C ABI. The only type related to boolean in e.g. the
> SysV ABI is _Bool, which is not a first-class type.
>

FWIW since C99, _Bool *is* in fact a basic type, defined to have a sizeof 1
and able to hold the values 0 and 1; additionally conversion of any nonzero
value from any type converts to 1 (this is opposed to, say, float which
would convert 0.5 to (int)1 but (_Bool)0).

Are there really (or are there likely ever to be) execution models that can
reasonably support packed boolean arrays particularly?

-- 
- DML • he/him