Up slide

Lbl Right
.r₁=row scan offset
.r₂=column scan index
.r₃=column dest index
.r₄=last value slid
 3
.For each row
 For(4)
  →r₁
  0→r₄
  12→r₃
  .For each column, starting from the right
  For(4)
   →r₂
   .If occupied by a tile
   If {+r₁+L₁}
    .Remove original tile
    Select(→r₅,0→{r₁+r₂+L₁})
    .If equal to the last slid tile
    !If -r₄
     .Increment merged tile value
     {r₁+r₃+4+L₁}++
    .If not equal to the last slid tile
    Else
     .Store tile to destination and decrement destination index
     Select(r₅,→{r₃-4→r₃+r₁+4+L₁})
    End
    .Store value last slid (or garbage if a merge occured)
    →r₄
   End
   r₂-4
  End
  r₁-1
 End
Return