WIP (Move index limit matching to the top)

It gives great speedup for complex structures while degrade
performance for plain long collections (though, it is still way faster than
original).

lib/msgpax/unpacker.ex

@@ -83,35 +83,35 @@ defmodule Msgpax.Unpacker do
 
   import Macro, only: [pipe: 3]
 
+  defp unpack(<<buffer::bits>>, result, options, [kind, index, size | outer], count, count) do
+    unpack(buffer, build_collection(result, count, kind), options, outer, index + 1, size)
+  end
+
   for {format, {:value, value}} <- formats do
-    defp unpack(<<unquote_splicing(format), rest::bits>>, result, options, outer, index, count) when index < count do
+    defp unpack(<<unquote_splicing(format), rest::bits>>, result, options, outer, index, count) do
       unpack(rest, [unquote(value) | result], options, outer, index + 1, count)
     end
   end
 
   for {format, {:call, call}} <- formats do
     options = Macro.var(:options, nil)
-    defp unpack(<<unquote_splicing(format), rest::bits>>, result, options, outer, index, count) when index < count do
+    defp unpack(<<unquote_splicing(format), rest::bits>>, result, options, outer, index, count) do
       unpack(rest, [unquote(pipe(options, call, 0)) | result], options, outer, index + 1, count)
     end
   end
 
   for {format, {:collection, :list = kind}} <- formats do
-    defp unpack(<<unquote_splicing(format), rest::bits>>, result, options, [kind | outer], index, count) when index < count do
-      unpack(rest, result, options, [unquote(kind), {kind, index, count} | outer], 0, unquote(quote(do: len)))
+    defp unpack(<<unquote_splicing(format), rest::bits>>, result, options, outer, index, count) do
+      unpack(rest, result, options, [unquote(kind), index, count | outer], 0, unquote(quote(do: len)))
     end
   end
 
   for {format, {:collection, :map = kind}} <- formats do
-    defp unpack(<<unquote_splicing(format), rest::bits>>, result, options, [kind | outer], index, count) when index < count do
-      unpack(rest, result, options, [unquote(kind), {kind, index, count} | outer], 0, unquote(quote(do: len)) * 2)
+    defp unpack(<<unquote_splicing(format), rest::bits>>, result, options, outer, index, count) do
+      unpack(rest, result, options, [unquote(kind), index, count | outer], 0, unquote(quote(do: len)) * 2)
     end
   end
 
-  defp unpack(<<buffer::bits>>, result, options, [kind, {next, index, size} | outer], count, count) do
-    unpack(buffer, build_collection(result, count, kind), options, [next | outer], index + 1, size)
-  end
-
   defp unpack(<<byte, _::bits>>, [], _options, _outer, _index, _count) do
     throw {:bad_format, byte}
   end