void b2Contact::Update()

in Box2D/Dynamics/Contacts/b2Contact.cpp [161:247]
68 lines of code
17 McCabe index (conditional complexity)

void b2Contact::Update(b2ContactListener* listener)
{
	b2Manifold oldManifold = m_manifold;

	// Re-enable this contact.
	m_flags |= e_enabledFlag;

	bool touching = false;
	bool wasTouching = (m_flags & e_touchingFlag) == e_touchingFlag;

	bool sensorA = m_fixtureA->IsSensor();
	bool sensorB = m_fixtureB->IsSensor();
	bool sensor = sensorA || sensorB;

	b2Body* bodyA = m_fixtureA->GetBody();
	b2Body* bodyB = m_fixtureB->GetBody();
	const b2Transform& xfA = bodyA->GetTransform();
	const b2Transform& xfB = bodyB->GetTransform();

	// Is this contact a sensor?
	if (sensor)
	{
		const b2Shape* shapeA = m_fixtureA->GetShape();
		const b2Shape* shapeB = m_fixtureB->GetShape();
		touching = b2TestOverlap(shapeA, m_indexA, shapeB, m_indexB, xfA, xfB);

		// Sensors don't generate manifolds.
		m_manifold.pointCount = 0;
	}
	else
	{
		Evaluate(&m_manifold, xfA, xfB);
		touching = m_manifold.pointCount > 0;

		// Match old contact ids to new contact ids and copy the
		// stored impulses to warm start the solver.
		for (int32 i = 0; i < m_manifold.pointCount; ++i)
		{
			b2ManifoldPoint* mp2 = m_manifold.points + i;
			mp2->normalImpulse = 0.0f;
			mp2->tangentImpulse = 0.0f;
			b2ContactID id2 = mp2->id;

			for (int32 j = 0; j < oldManifold.pointCount; ++j)
			{
				b2ManifoldPoint* mp1 = oldManifold.points + j;

				if (mp1->id.key == id2.key)
				{
					mp2->normalImpulse = mp1->normalImpulse;
					mp2->tangentImpulse = mp1->tangentImpulse;
					break;
				}
			}
		}

		if (touching != wasTouching)
		{
			bodyA->SetAwake(true);
			bodyB->SetAwake(true);
		}
	}

	if (touching)
	{
		m_flags |= e_touchingFlag;
	}
	else
	{
		m_flags &= ~e_touchingFlag;
	}

	if (wasTouching == false && touching == true && listener)
	{
		listener->BeginContact(this);
	}

	if (wasTouching == true && touching == false && listener)
	{
		listener->EndContact(this);
	}

	if (sensor == false && touching && listener)
	{
		listener->PreSolve(this, &oldManifold);
	}
}