Function for traversing a matrix over its diagonals

gistfile1.js

function diagonalTraverse(m, fn)
{
    // This only works for rectangular or square
    // form matrices. So no rows of variable sizes!

    if ( m && m.length > 0 && m[0].length > 0 )
    {
        var i = 0, j = 0,
            ci = null, cj = null,
            M = m[i].length, // # of columns
            N = m.length - 1; // # of rows
        while ( i < M || j < N )
        {
            // invariant:
            //   0 <= i <= m.size.x
            //   0 <= j <= m.size.y - 1

            ci = i, cj = j;
            while ( ci < M - 1 && cj > 0 )
            {
                // invariant:
                //   i <= ci < M - 1
                //   j >= cj >= 0

                fn(m[cj][ci], cj, ci);

                ci++;
                cj--;
            }

            fn(m[cj][ci], cj, ci);

            if ( j < N )
                j++;
            else
                i++;
        }
    }
}

gistfile2.py

def high_triangular_traverse(m, f):
    """fugly but curious that only requires some minor var swaps..."""
    i = j = 0
    ci = cj = None
    M = N = len(m)
    N -= 1
    while i < M or j < N:
        cj = i
        ci = j
        while ci < (M - 1) and cj > 0:
            f(m[cj][ci], cj, ci)
            cj += 1
            ci -= 1
        f(m[cj][ci], cj, ci)
        if j < N:
            j += 1
        else:
            i += 1