Speed up Array#split

Benchmark:
          user     system      total        real
old   0.510000   0.000000   0.510000 (  0.506749)
new   0.330000   0.000000   0.330000 (  0.336187)

1 files changed, 20 insertions, 6 deletions

diff --git a/activesupport/lib/active_support/core_ext/array/grouping.rb b/activesupport/lib/active_support/core_ext/array/grouping.rb
index dbddc7a7b4..36896f9614 100644
--- a/activesupport/lib/active_support/core_ext/array/grouping.rb
+++ b/activesupport/lib/active_support/core_ext/array/grouping.rb
@@ -86,13 +86,27 @@ class Array
   #   [1, 2, 3, 4, 5].split(3)              # => [[1, 2], [4, 5]]
   #   (1..10).to_a.split { |i| i % 3 == 0 } # => [[1, 2], [4, 5], [7, 8], [10]]
   def split(value = nil, &block)
-    inject([[]]) do |results, element|
-      if block && block.call(element) || value == element
-        results << []
-      else
-        results.last << element
-      end
+    if block
+      inject([[]]) do |results, element|
+        if block.call(element)
+          results << []
+        else
+          results.last << element
+        end
 
+        results
+      end
+    else
+      results, arr = [[]], self
+      until arr.empty?
+        if (idx = index(value))
+          results.last.concat(arr.shift(idx))
+          arr.shift
+          results << []
+        else
+          results.last.concat(arr.shift(arr.size))
+        end
+      end
       results
     end
   end