2018-04-19 10:24 GMT+02:00 Serge Stinckwich <serge.stinckwich@gmail.com>:

On Thu, Apr 19, 2018 at 9:13 AM, Serge Stinckwich <serge.stinckwich@gmail.com> wrote:

I try to understand differences between 32 bits and 64 bits FFI support for C structures.

I build a class called MyStruct subclass of FFIExternalStructure.

and define a layout for this structure like this one :

MyStruct class>>fieldsDesc
������ "self rebuildFieldAccessors"

������ ^ #(
������ ������ int index ;)

and then I generate automatically the field accessors.

If I use a 32 bit VM, the following method is generated to access the index field :

index
������ "This method was automatically generated"
������ ^handle signedLongAt: OFFSET_INDEX

and if I use a 64 bits VM, the same method is generated ...

I'm a bit puzzled because, if sizeof(int) = sizeof(long) in a 32 bits VM, they have different for 64 bits VM (sizeof(int) = 4 and sizeof(long) = 8).

Someone to explain me or this is a bug ?

���Ok I have understood ...

signedLongAt: method does not return a long as the name seems to indicate but in fact a 32 bits integer.

So it works in both 32 and 64 bits VM.

Maybe signedInt32At: would have been a better name :-) ���

Maybe this is because long in C does not guarantee 64bits, only long long does.

Thierry

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--

Serge Stinckwich
UMI UMMISCO 209 (SU/IRD/UY1)

"Programs must be written for people to read, and only incidentally for machines to execute."

http://www.doesnotunderstand.org/