now it actually works!

autobrake_test.p8

@@ -130,7 +130,7 @@ function ship:draw()
  if (self.dx == 0) return
  local bd, f = brake_dist(self.dx, self.thrust + self.drag)
  local bdx = self.x+bd-2
- spr(3, bdx,self.y-3)
+ spr(3, bdx,self.y-2)
  print(tostr(f), bdx, self.y - 8, 14)
 end
 
@@ -177,11 +177,11 @@ function constraints:constrain(s, want)
 end
 
 function brake_dist(v0, brake_max)
- local tri_frames = abs(v0/brake_max)&-1
+ local tri_frames = abs(v0\brake_max)
  local chunks = tri_frames * (tri_frames - 1) >> 1
  local chunk_zone = chunks * brake_max
- local overage = v0 - tri_frames * brake_max
- return (chunk_zone + overage * (tri_frames + 1)) * -sgn(v0), (overage > 0) and tri_frames + 1 or tri_frames
+ local overage = abs(v0) - tri_frames * brake_max
+ return (chunk_zone + overage * (tri_frames + 1)) * sgn(v0), (overage > 0) and tri_frames + 1 or tri_frames
 end
 
 function constraints:cycle()