invert eship/pbullet collision

Also mildly trims up linked_list impl.

vacuum_gambit.p8

@@ -60,7 +60,7 @@ function mknew(tt)
 end
 
 -- intrusive singly-linked list.
--- cannot be nested!
+-- cannot be nested or crossed!
 linked_list = mknew{
  is_linked_list=true,
  init = function(x)
@@ -93,9 +93,7 @@ end
 
 -- strip calls f(x) for each
 -- node, removing each node for
--- which f(x) returns true. it
--- returns the new tail; nil
--- if the list is now empty.
+-- which f(x) returns true.
 function linked_list:strip(f)
  local p, n = self, self.next
  while n do
@@ -107,7 +105,6 @@ function linked_list:strip(f)
   n = n.next
  end
  self.tail = p
- return p
 end
 
 -- optimized special case -
@@ -258,31 +255,35 @@ function updategame()
 
 	-- many bullets and many enemy ships;
 	-- use bucket collider for efficiency
- local pbullet_collider = collider.new()
- local p, n = pbullets, pbullets.next
+
+ local eship_collider = collider.new()
+ -- save tokens, lose time:
+ -- eships:strip(function(s) eship_collider:insert(s) end)
+ local p, n = eships, eships.next
  while n do
   n.prev = p
-  pbullet_collider:insert(n)
+  eship_collider:insert(n)
   p = n
   n = p.next
  end
 
- eships:strip(
-  function(es)
-   for pb in all(pbullet_collider:get_collisions(es)) do
-    if pb:hitship(es) then
-     pbullet_collider:hide(pb)
-     pb.prev.next = pb.next
-     if pb.next then
-      pb.next.prev = pb.prev
+ -- lose tokens, save time:
+ -- unroll `strip` to avoid
+ -- function call overhead
+ pbullets:strip(function(pb)
+  for es in all(eship_collider:get_collisions(pb)) do
+   if es:hitbullet(pb) then
+    eship_collider:hide(es)
+    es.prev.next=es.next
+    if es.next then
+     es.next.prev = es.prev
     else
-      pbullets.tail = pb.prev
+     eships.tail = es.prev
     end
    end
-    if (es:hitbullet(pb)) return true
+   if (pb:hitship(es)) return true
   end
-  end
- )
+ end)
  
  intangibles_fg:strip(call_move)