Implemented the ie-hex-str built-in function.

Author: Aaron Leung

context.cpp

@@ -144,7 +144,8 @@ namespace Sass {
     // Other Color Functions
     register_function(adjust_color_sig, adjust_color);
     register_function(scale_color_sig, scale_color);
-    register_function(change_color_sig, change_color);    
+    register_function(change_color_sig, change_color);   
+    register_function(ie_hex_str_sig, ie_hex_str); 
     // String Functions
     register_function(unquote_sig, unquote);
     register_function(quote_sig, quote);

functions.cpp

@@ -737,6 +737,16 @@ namespace Sass {
       return Node();
     }
 
+    extern Signature ie_hex_str_sig = "ie-hex-str($color)";
+    Node ie_hex_str(const Node parameter_names, Environment& bindings, Node_Factory& new_Node, Backtrace& bt, string& path, size_t line) {
+      Node color(arg(ie_hex_str_sig, path, line, parameter_names, bindings, 0, Node::numeric_color, bt));
+      Node result(new_Node(Node::ie_hex_str, color.path(), color.line(), 4));
+      result << color[0] << color[1] << color[2] << color[3];
+      Node wrapped_result(new_Node(Node::concatenation, color.path(), color.line(), 1));
+      wrapped_result << result;
+      return wrapped_result;
+    }
+
     ////////////////////////////////////////////////////////////////////////
     // String Functions ////////////////////////////////////////////////////
     ////////////////////////////////////////////////////////////////////////

functions.hpp

@@ -158,6 +158,9 @@ namespace Sass {
     extern Signature change_color_sig;
     Node change_color(const Node, Environment&, Node_Factory&, Backtrace&, string& path, size_t line);
 
+    extern Signature ie_hex_str_sig;
+    Node ie_hex_str(const Node, Environment&, Node_Factory&, Backtrace&, string& path, size_t line);
+
     // String Functions ////////////////////////////////////////////////////
 
     extern Signature unquote_sig;

node.hpp

@@ -142,6 +142,7 @@ namespace Sass {
       numeric_percentage,
       numeric_dimension,
       numeric_color,
+      ie_hex_str,
       boolean,
       important,
 

node_emitters.cpp

@@ -278,6 +278,25 @@ namespace Sass {
           return ss.str();
         }
       } break;
+
+      case ie_hex_str: {
+        stringstream ss;
+        ss << '#' << std::setw(2) << std::setfill('0') << std::hex;
+
+        double x = at(3).numeric_value() * 255;
+        if (x > 0xff) x = 0xff;
+        else if (x < 0) x = 0;
+        ss << std::hex << std::setw(2) << std::uppercase << static_cast<unsigned long>(std::floor(x+0.5));
+
+        for (size_t i = 0; i < 3; ++i) {
+          double x = at(i).numeric_value();
+          if (x > 0xff) x = 0xff;
+          else if (x < 0) x = 0;
+          ss << std::hex << std::setw(2) << std::uppercase << static_cast<unsigned long>(std::floor(x+0.5));
+        }
+
+        return ss.str();
+      } break;
 
       case uri: {
         string result("url(");