How to cast simple pointer to a multidimensional-array of fixed size?

Question

I have a function that takes a pointer to a floating point array. Based on other conditions, I know that pointer is actually pointing to a 2x2 OR 3x3 matrix. (in fact the memory was initially allocated as such, e.g. float M[2][2] ) The important thing is I want to make this determination in the function body, not as the function argument.

void calcMatrix( int face, float * matrixReturnAsArray )
{
    // Here, I would much rather work in natural matrix notation
    if( is2x2 )
    {
        // ### cast matrixReturnAsArray to somethingAsMatrix[2][2]
        somethingAsMatrix[0][1] = 2.002;
        // etc..
    }
    else if(is3x3)
    { //etc...
    }

}

I am aware that I could use templates and other techniques to better address this problem. My question is really about how to make such a cast at the ### comment. Working in C++.

Answer 1

float (*somethingAsMatrix)[2] = (float (*)[2]) matrixReturnAsArray;