Fix bugs in binary_slice/2 (#12045)

Author: sabiwara

lib/elixir/lib/kernel.ex

@@ -4649,29 +4649,22 @@ defmodule Kernel do
       when is_binary(binary) and step > 0 do
     total = byte_size(binary)
 
-    first =
-      case first < 0 do
-        true -> max(first + total, 0)
-        false -> first
-      end
+    first = if first < 0, do: max(first + total, 0), else: first
+    last = if last < 0, do: last + total, else: last
 
-    last =
-      case last < 0 do
-        true -> last + total
-        false -> last
-      end
+    amount = last - first + 1
 
-    case first < total do
-      true ->
-        part = binary_part(binary, first, min(total - first, last - first + 1))
-
-        case step do
-          1 -> part
-          _ -> for <<byte, _::size(step - 1)-bytes <- part>>, into: "", do: <<byte>>
-        end
+    if first < total and amount > 0 do
+      part = binary_part(binary, first, min(amount, total - first))
 
-      false ->
-        ""
+      if step == 1 do
+        part
+      else
+        <<first_byte, rest::binary>> = part
+        for <<_::size(step - 1)-bytes, byte <- rest>>, into: <<first_byte>>, do: <<byte>>
+      end
+    else
+      ""
     end
   end
 

lib/elixir/test/elixir/kernel_test.exs

@@ -1424,6 +1424,13 @@ defmodule KernelTest do
     assert match?(x when ceil(x) == 1, 0.2)
   end
 
+  test "binary_slice/2" do
+    assert binary_slice("abc", -1..0) == ""
+    assert binary_slice("abc", -5..-5) == ""
+    assert binary_slice("x", 0..0//2) == "x"
+    assert binary_slice("abcde", 1..3//2) == "bd"
+  end
+
   test "sigil_U/2" do
     assert ~U[2015-01-13 13:00:07.123Z] == %DateTime{
              calendar: Calendar.ISO,