Help condensing nested if blocks

[axcho]

I am writing a particle physics engine, and I have a fairly verbose section of code to calculate relative masses when there are massless particles involved. It seems like it should be reducible down to some concise math and fewer if statements. Can you suggest any ways to do this? I'd appreciate the help.

m -> a mass
w -> an inverse mass (1/m) used by the physics engine

when w = 0, the particle has infinite mass and does not move
when w > 0, the particle has some normal amount of mass, unless...

unless m = 0, in which case the particle has no mass
so w values for the other particles must be adjusted to compensate

Here's the relevant code:

// calculate relative node weights
var w0:Number = n0.w;		// node 0 weight
var w1:Number = n1.w;		// node 1 weight
var w2:Number = n2.w;		// node 2 weight

// check whether nodes are weightless
if ( n0.m )
{
	if ( n1.m )
	{
		if ( n2.m )
		{
			// keep weights as they are
		}
		else
		{
			// only node 2 should move
			w0 = w1 = 0;
			w2 = 1;
		}
	}
	else
	{
		if ( n2.m )
		{
			// only node 1 should move
			w0 = w2 = 0;
			w1 = 1;
		}
		else
		{
			// node 1 and node 2 should move
			w0 = 0;
			w1 = w2 = 1;
		}
	}
}
else
{
	if ( n1.m )
	{
		if ( n2.m )
		{
			// only node 0 should move
			w1 = w2 = 0;
			w0 = 1;
		}
		else
		{
			// node 0 and node 2 should move
			w1 = 0;
			w0 = w2 = 1;
		}
	}
	else
	{
		if ( n2.m )
		{
			// node 0 and node 1 should move
			w2 = 0;
			w0 = w1 = 1;
		}
		else
		{
			// all nodes are equal
			w0 = w1 = w2 = 1;
		}
	}
}

Thanks in advance!