use Zlib.crc2 rather that bytes.sum, as per Aaron's suggestion

That integer is rather irrelevant, the only thing that matters is that
it is consistent and with no apparent bias. Zlib.crc32 is 8-10 times
faster than bytes.sum, so use that.

actionpack/lib/action_view/asset_paths.rb

@@ -1,3 +1,4 @@
+require 'zlib'
 require 'active_support/core_ext/file'
 
 module ActionView
@@ -111,8 +112,7 @@ module ActionView
           args << current_request if (arity > 1 || arity < 0) && has_request?
           host.call(*args)
         else
-          source_num = source.bytes.sum
-          (host =~ /%d/) ? host % (source_num % 4) : host
+          (host =~ /%d/) ? host % (Zlib.crc32(source) % 4) : host
         end
       end
     end

actionpack/test/template/asset_tag_helper_test.rb

@@ -1,3 +1,4 @@
+require 'zlib'
 require 'abstract_unit'
 require 'active_support/ordered_options'
 
@@ -689,7 +690,7 @@ class AssetTagHelperTest < ActionView::TestCase
     @controller.config.asset_host = 'http://a%d.example.com'
     config.perform_caching = true
 
-    number = '/javascripts/cache/money.js'.bytes.sum % 4
+    number = Zlib.crc32('/javascripts/cache/money.js') % 4
     assert_dom_equal(
       %(<script src="http://a#{number}.example.com/javascripts/cache/money.js" type="text/javascript"></script>),
       javascript_include_tag(:all, :cache => "cache/money")