Fix broadphase warnings for clang (some conversion remain for g++)

[wxmerkt]

No description provided.

[jcarpent]

I don't have any warning on my side. Could you give me the compiler and its version in use?

[wxmerkt]

clang10 on Ubuntu 20.04:

clang version 10.0.0-4ubuntu1 
Target: x86_64-pc-linux-gnu

[jcarpent]

OK. I will accept it, even if I think this is a mistake from your compiler or maybe the Eigen version in use.
Normally, such an operation should not need a cast as the vector is made of double values.

[jmirabel]

By curiosity, can you check if you have a warning with an int instead of a long.

[wxmerkt]

@jmirabel Indeed, I didn't see the warning in that case. Note, however that then we'd need to use a cast from long to int above.

[jmirabel]

Then I think it depends on the size of long your compiler uses.

Although minor to me and questionable, I think it makes more sense to use int (with a static cast). I don't think we will ever reach 2^31 leaves (except may be on very particular setup).

[jcarpent]

I do think that the issue is coming from your compiler. I don't have such warnings with clang 13.0

[jmirabel]

It does not depend only on the compiler. If you want to be sure it's the compiler fault, you should check that sizeof(long) is the same with both setup.