Optimize Kernel.binary_slice/2 for stepped ranges (#15989)

Author: preciz

lib/elixir/lib/kernel.ex

@@ -5045,13 +5045,19 @@ defmodule Kernel do
     amount = last - first + 1
 
     if first < total and amount > 0 do
-      part = binary_part(binary, first, min(amount, total - first))
+      length = min(amount, total - first)
 
-      if step == 1 do
-        part
-      else
-        <<first_byte, rest::binary>> = part
-        for <<_::size(^step - 1)-bytes, byte <- rest>>, into: <<first_byte>>, do: <<byte>>
+      cond do
+        step == 1 ->
+          binary_part(binary, first, length)
+
+        length <= step ->
+          binary_part(binary, first, 1)
+
+        true ->
+          <<first_byte, rest::binary>> = binary_part(binary, first, length)
+          skip = step - 1
+          for <<_::size(^skip)-bytes, byte <- rest>>, into: <<first_byte>>, do: <<byte>>
       end
     else
       ""