[eigen] Possible undefined behavior in insert() in SparseMatrix

[Jens Mueller <jens.k.mueller@xxxxxx>]

Hi,

I justed checked the new insert() method for the SparseMatrix. There
seems to be a problem, if the actual size is 0. So assuming you created
a new sparse matrix and ran setZero() but no reserve(). And then you
start inserting. In that case line 251 in SparseMatrix results in a nan
(due to division by zero). And the following std::max and std::min
operations have undefined behavior when passing a nan. In my case I get
a nan as value for reallocRatio. And this may result in
CompressedStorage's resize to allocate really much memory.
For me I even get a std::bad_alloc, if my Scalar type is an unsigned
char (checked attached code). For some reason I don't get it for int.
This is strange to me. But another issue I don not understand yet.

Regards,
Jens

#include <Eigen/Sparse>

namespace Eigen {

template<> struct NumTraits<unsigned char>
{
  typedef unsigned char Real;
  typedef double FloatingPoint;
  enum {
    IsComplex = 0,
    HasFloatingPoint = 0,
    ReadCost = 1,
    AddCost = 1,
    MulCost = 1
  };
};

}

int main() {

	// for int it works
	Eigen::SparseMatrix<unsigned char> foo(10,10);

	foo.setZero();
	//foo.reserve(1);
	// next line results in std::bad_alloc on line 211 of CompressedStorage.h
	// but not for int as Scalar?
	foo.insert(2,3) = 4;
	foo.finalize();
}