Re: Using function from .cpp in .ispc

[Matt Pharr]

The trick is that functions called from ispc should have "C" linkage, and not have C++ name mangling applied.

So, if you add this line to the start of a.cpp:

extern "C" { int foo(); }

Then foo() will be C-callable and everything should work as expected.

Thanks,

Matt

On Tue, Apr 16, 2013 at 4:02 PM, Martin Šošić <sosic....@gmail.com> wrote:

Hi everybody, I have a problem trying to use function from a.cpp in b.ispc.
I read from guide about using extern for this but I keep getting errors.
I did following:
a.cpp:
    int foo() {return 1};
    int main() {
        ispc::simple();
    }

b.ispc:
    extern int foo();
    export void simple() {
        print("%d\n", foo());
    }

This is the error message i get:
simple_ispc.o: In function `simple___':
simple.ispc:(.text+0x939): undefined reference to `foo___'
simple_ispc.o: In function `simple':
simple.ispc:(.text+0x979): undefined reference to `foo___'
collect2: error: ld returned 1 exit status

What am I doing wrong, maybe this is not possible? If not what do you suggest, what are other options?
Thank you

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[Dmitry Babokin]

Martin,

Here's an example:

> cat a.cpp 

#include "b.h"

extern "C" int foo() {return 1;}

int main() {

    ispc::simple();

}

> cat b.cpp 

extern "C" uniform int foo();

export void simple() {

    print("%\n", foo());

}

> ispc b.cpp --target=sse4 -o b.o -h b.h

> g++ -c a.cpp

> g++ a.o b.o

> a.out 

1

Also note that formatting of print string is slightly different from printf strings: http://ispc.github.io/ispc.html#output-functions 

[Martin Šošić]

Thank you both, that works!
Do you maybe have any advice how to export functions that are private methods of class? I guess that is not possible?

[Dmitry Babokin]

I'm not sure that you can have "extern "C"" linkage for any class member (regardless it's private or public). So you have to have C-style interface to interract with ispc code.

[Matt Pharr]

You could do this with a forwarding function--e.g.

class Foo {

private:

  void bar();

  friend void FooBar(Foo *);

};

extern "C" void FooBar(Foo *f) {

  f->bar();

}

and then you can call FooBar() with a Foo * uniform pointer from ispc...

Thanks,

Matt