Improve perf of ActionView::Helpers::TextHelper#excerpt for large strings.

Author: tgxworld

actionview/lib/action_view/helpers/text_helper.rb

@@ -1,6 +1,7 @@
 # frozen_string_literal: true
 
 require "active_support/core_ext/string/filters"
+require "active_support/core_ext/string/access"
 require "active_support/core_ext/array/extract_options"
 
 module ActionView
@@ -467,18 +468,25 @@ def cut_excerpt_part(part_position, part, separator, options)
           radius   = options.fetch(:radius, 100)
           omission = options.fetch(:omission, "...")
 
-          part = part.split(separator)
-          part.delete("")
-          affix = part.size > radius ? omission : ""
+          if separator != ""
+            part = part.split(separator)
+            part.delete("")
+          end
 
-          part = if part_position == :first
-            drop_index = [part.length - radius, 0].max
-            part.drop(drop_index)
-          else
-            part.first(radius)
+          affix = part.length > radius ? omission : ""
+
+          part =
+            if part_position == :first
+              part.last(radius)
+            else
+              part.first(radius)
+            end
+
+          if separator != ""
+            part = part.join(separator)
           end
 
-          return affix, part.join(separator)
+          return affix, part
         end
     end
   end