Greatly increased performance of String.to_json, which speeds up RJS considerably on large pages, fixes #3473 [Shugo Maeda]

git-svn-id: http://svn-commit.rubyonrails.org/rails/trunk@4787 5ecf4fe2-1ee6-0310-87b1-e25e094e27de

activesupport/CHANGELOG

@@ -1,5 +1,7 @@
 *SVN*
 
+* Greatly increased performance of String.to_json, which speeds up RJS considerably on large pages, fixes #3473 [Shugo Maeda]
+
 * Detect missing_constants calls from removed modules and fail accordingly. [Nicholas Seckar]
 
 * Stop using defined? in Dependencies.qualified_const_defined? since defined? may invoke const_missing. [Nicholas Seckar]

activesupport/lib/active_support/json/encoders/core.rb

@@ -16,24 +16,25 @@ module Encoders #:nodoc:
       define_encoder NilClass do
         'null'
       end
+
+      ESCAPED_CHARS = {
+        "\010" =>  '\b',
+        "\f" =>    '\f',
+        "\n" =>    '\n',
+        "\r" =>    '\r',
+        "\t" =>    '\t',
+        '"' =>     '\"',
+        '\\' =>    '\\\\'
+      }
       
       define_encoder String do |string|
-        returning value = '"' do
-          string.each_char do |char|
-            value << case
-            when char == "\010":  '\b'
-            when char == "\f":    '\f'
-            when char == "\n":    '\n'
-            when char == "\r":    '\r'
-            when char == "\t":    '\t'
-            when char == '"':     '\"'
-            when char == '\\':    '\\\\'  
-            when char.length > 1: "\\u#{'%04x' % char.unpack('U').first}"
-            else;                 char
-            end
-          end
-          value << '"'
-        end
+        '"' + string.gsub(/[\010\f\n\r\t"\\]/) { |s|
+          ESCAPED_CHARS[s]
+        }.gsub(/([\xC0-\xDF][\x80-\xBF]|
+                 [\xE0-\xEF][\x80-\xBF]{2}|
+                 [\xF0-\xF7][\x80-\xBF]{3})+/ux) { |s|
+          s.unpack("U*").pack("n*").unpack("H*")[0].gsub(/.{4}/, '\\\\u\&')
+        } + '"'
       end
       
       define_encoder Numeric do |numeric|