void Swap(ref float lhs, ref float rhs)
{
    float tmp = lhs;
    lhs = rhs;
    rhs = tmp;
}

void InplaceFlipX(float[,] arr)
{
    int rowLength = arr.GetLength(1);
    for (int ix = 0; ix < arr.GetLength(0); ix++)   // rows
        for (int jx = 0; jx < rowLength / 2; jx++)   // columns
            Swap(ref arr[ix, jx], ref arr[ix, rowLength - jx - 1]);
}

void InplaceFlipY(float[,] arr)
{
    int columnLength = arr.GetLength(0);
    for (int ix = 0; ix < arr.GetLength(1); ix++)	// rows
        for (int jx = 0; jx < columnLength / 2; jx++)	// columns
            Swap(ref arr[jx, ix], ref arr[columnLength - jx - 1, ix]);
}

private void InplaceFlipX(float[,,] arr)
{
    int rowLength = arr.GetLength(1);
    for (int ix = 0; ix < arr.GetLength(0); ix++)   // rows
        for (int jx = 0; jx < rowLength / 2; jx++)   // columns
            for (int kx = 0; kx < arr.GetLength(2); kx++)
                Swap(ref arr[ix, jx, kx], ref arr[ix, rowLength - jx - 1, kx]);
}

private void InplaceFlipY(float[,,] arr)
{
    int columnLength = arr.GetLength(0);
    for (int ix = 0; ix < arr.GetLength(1); ix++)   // rows
        for (int jx = 0; jx < columnLength / 2; jx++)   // columns
            for (int kx = 0; kx < arr.GetLength(2); kx++)
                Swap(ref arr[jx, ix, kx], ref arr[columnLength - jx - 1, ix, kx]);
}


void Main()
{
	var foo = new float[2, 3]
    {
    	{1,2,3},
        {4,5,6},
    };

	foo.Dump();
	InplaceFlipX(foo);
	foo.Dump();
	InplaceFlipY(foo);
	foo.Dump();

	var boo = new float [2,3,2] {
		{ {1,2}, {2,3}, {3,4} },
		{ {4,5}, {5,6}, {6,7} },
	};

	boo.Dump();
	InplaceFlipX(boo);
	boo.Dump();
	InplaceFlipY(boo);
	boo.Dump();

}