Swig and Octave under Windows (mingw64) / long is only 32 bit

I tried creating some oct file for Octave under Windows (mingw64).
SWIG was installed using msys2 ( msys2-x86_64-20190524.exe );
 pacman -S mingw64/mingw-w64-x86_64-swig
octave was installed from binaries ( octave-5.1.0-w64-installer )
 
I created the wrapper file "xxx_wrap.cxx" using
 
swig -octave -c++
 
and then compiled with
 
mkoctfile  xxx_wrap.cxx
 
Then I get the error message
 
xxx_wrap.cxx: In member function 'long int octave_swig_type::swig_this() const':
xxx_wrap.cxx:1380:16: error: cast from 'const octave_swig_type*' to 'long int' loses precision [-fpermissive]
  return (long) this;
                ^~~~
xxx_wrap.cxx:1381:37: error: cast from 'void*' to 'long int' loses precision [-fpermissive]
       return (long) types[0].second.ptr;
 
When I manually change from "long" to "long long" in xxx_wrap.cxx it compiles fine and creates a working .oct file:
 
    long long swig_this() const {
      if (!types.size())
    return (long long) this;
      return (long long) types[0].second.ptr;
    }
 
As I understand, the problem is that in mingw64-gcc "long" is only 32 bit (for Visual C++ compatibility), but pointers are 64 bit.
 
Is there a SWIG version/option to fix this automatically?
 
Helmut


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