Optimize Float.parse/1 (#14159)

Author: dkuku

lib/elixir/lib/float.ex

@@ -164,40 +164,50 @@ defmodule Float do
   end
 
   defp parse_unsigned(<<digit, rest::binary>>) when digit in ?0..?9,
-    do: parse_unsigned(rest, false, false, <<digit>>)
+    do: parse_unsigned(rest, false, false, [digit])
 
   defp parse_unsigned(binary) when is_binary(binary), do: :error
 
   defp parse_unsigned(<<digit, rest::binary>>, dot?, e?, acc) when digit in ?0..?9,
-    do: parse_unsigned(rest, dot?, e?, <<acc::binary, digit>>)
+    do: parse_unsigned(rest, dot?, e?, [digit | acc])
 
   defp parse_unsigned(<<?., digit, rest::binary>>, false, false, acc) when digit in ?0..?9,
-    do: parse_unsigned(rest, true, false, <<acc::binary, ?., digit>>)
+    do: parse_unsigned(rest, true, false, [digit, ?. | acc])
 
   defp parse_unsigned(<<exp_marker, digit, rest::binary>>, dot?, false, acc)
        when exp_marker in ~c"eE" and digit in ?0..?9,
-       do: parse_unsigned(rest, true, true, <<add_dot(acc, dot?)::binary, ?e, digit>>)
+       do: parse_unsigned(rest, true, true, [digit, ?e | add_dot(acc, dot?)])
 
   defp parse_unsigned(<<exp_marker, sign, digit, rest::binary>>, dot?, false, acc)
        when exp_marker in ~c"eE" and sign in ~c"-+" and digit in ?0..?9,
-       do: parse_unsigned(rest, true, true, <<add_dot(acc, dot?)::binary, ?e, sign, digit>>)
+       do: parse_unsigned(rest, true, true, [digit, sign, ?e | add_dot(acc, dot?)])
 
   # When floats are expressed in scientific notation, :erlang.binary_to_float/1 can raise an
   # ArgumentError if the e exponent is too big. For example, "1.0e400". Because of this, we
   # rescue the ArgumentError here and return an error.
   defp parse_unsigned(rest, dot?, true = _e?, acc) do
-    :erlang.binary_to_float(add_dot(acc, dot?))
+    acc
+    |> add_dot(dot?)
+    |> :lists.reverse()
+    |> :erlang.list_to_float()
   rescue
     ArgumentError -> :error
   else
     float -> {float, rest}
   end
 
-  defp parse_unsigned(rest, dot?, false = _e?, acc),
-    do: {:erlang.binary_to_float(add_dot(acc, dot?)), rest}
+  defp parse_unsigned(rest, dot?, false = _e?, acc) do
+    float =
+      acc
+      |> add_dot(dot?)
+      |> :lists.reverse()
+      |> :erlang.list_to_float()
+
+    {float, rest}
+  end
 
   defp add_dot(acc, true), do: acc
-  defp add_dot(acc, false), do: acc <> ".0"
+  defp add_dot(acc, false), do: [?0, ?. | acc]
 
   @doc """
   Rounds a float to the largest float less than or equal to `number`.