Refactor implementation for String.prototype.replace.

src/string.js

Index: src/string.js
diff --git a/src/string.js b/src/string.js
index b39976c51ed8a15332eccabecc2d1c34e26cf962..7d81abbcfda4ecb32f2663a09f5e1ea149d7fe2f 100644
--- a/src/string.js
+++ b/src/string.js
@@ -229,60 +229,78 @@ function StringReplace(search, replace) {
   }
   var subject = TO_STRING_INLINE(this);
 
-  // Delegate to one of the regular expression variants if necessary.
+  // Decision tree for dispatch
+  // .. regexp search
+  // .... string replace
+  // ...... non-global search
+  // ........ empty string replace
+  // ........ non-empty string replace (with $-expansion)
+  // ...... global search
+  // ........ no need to circumvent last match info override
+  // ........ need to circument last match info override
+  // .... function replace
+  // ...... global search
+  // ...... non-global search
+  // .. string search
+  // .... special case that replaces with one single character
+  // ...... function replace
+  // ...... string replace (with $-expansion)
+
   if (IS_REGEXP(search)) {
-    // Emulate RegExp.prototype.exec's side effect in step 5, even though
+    // Emulate RegExp.prototype.exec's side effect in step 5, even if
     // value is discarded.
     ToInteger(search.lastIndex);
     %_Log('regexp', 'regexp-replace,%0r,%1S', [search, subject]);
-    if (IS_SPEC_FUNCTION(replace)) {
-      if (search.global) {
-        return StringReplaceGlobalRegExpWithFunction(subject, search, replace);
-      } else {
-        return StringReplaceNonGlobalRegExpWithFunction(subject,
-                                                        search,
-                                                        replace);
-      }
-    } else {
-      if (lastMatchInfoOverride == null) {
-        var answer = %StringReplaceRegExpWithString(subject,
-                                                    search,
-                                                    TO_STRING_INLINE(replace),
-                                                    lastMatchInfo);
-        if (IS_UNDEFINED(answer)) {  // No match.  Return subject string.
-          search.lastIndex = 0;
+
+    if (!IS_SPEC_FUNCTION(replace)) {
+      if (!search.global) {
+        // Non-global regexp search, string replace.
+        var match = DoRegExpExec(search, subject, 0);
+        if (match == null) {
+          search.lastIndex = 0
           return subject;
         }
-        if (search.global) search.lastIndex = 0;
-        return answer;
+        if (replace.length == 0) {
+          return SubString(subject, 0, match[CAPTURE0]) +
+                 SubString(subject, match[CAPTURE1], subject.length)
+        }
+        return ExpandReplacement(TO_STRING_INLINE(replace),
+                                 subject,
+                                 lastMatchInfo,
+                                 SubString(subject, 0, match[CAPTURE0])) +
+               SubString(subject, match[CAPTURE1], subject.length);

[ulan, 2013/02/05 09:30:58]

I would reformat by putting the first argument of ExpandReplacement in a new
line.

[Yang, 2013/02/05 10:47:32]

Not entirely sure what you mean here.

+      }
+
+      // Global regexp search, string replace.
+      search.lastIndex = 0;
+      if (lastMatchInfoOverride == null) {
+        return %StringReplaceGlobalRegExpWithString(
+            subject, search, replace, lastMatchInfo);
       } else {
         // We use this hack to detect whether StringReplaceRegExpWithString
         // found at least one hit. In that case we need to remove any
         // override.
         var saved_subject = lastMatchInfo[LAST_SUBJECT_INDEX];
         lastMatchInfo[LAST_SUBJECT_INDEX] = 0;
-        var answer = %StringReplaceRegExpWithString(subject,
-                                                    search,
-                                                    TO_STRING_INLINE(replace),
-                                                    lastMatchInfo);
-        if (IS_UNDEFINED(answer)) {  // No match.  Return subject string.
-          search.lastIndex = 0;
-          lastMatchInfo[LAST_SUBJECT_INDEX] = saved_subject;
-          return subject;
-        }
+        var answer = %StringReplaceGlobalRegExpWithString(
+            subject, search, replace, lastMatchInfo);
         if (%_IsSmi(lastMatchInfo[LAST_SUBJECT_INDEX])) {
           lastMatchInfo[LAST_SUBJECT_INDEX] = saved_subject;
         } else {
           lastMatchInfoOverride = null;
         }
-        if (search.global) search.lastIndex = 0;
         return answer;
       }
     }
+
+    if (search.global) {
+      // Global regexp search, function replace.
+      return StringReplaceGlobalRegExpWithFunction(subject, search, replace);
+    }
+    // Non-global regexp search, function replace.
+    return StringReplaceNonGlobalRegExpWithFunction(subject, search, replace);
   }
 
-  // Convert the search argument to a string and search for it.
-  search = TO_STRING_INLINE(search);

[ulan, 2013/02/05 09:30:58]

Looks like it was remove accidentally.

   if (search.length == 1 &&
       subject.length > 0xFF &&
       IS_STRING(replace) &&
@@ -342,6 +360,38 @@ function ExpandReplacement(string, subject, matchInfo, result) {
       } else if (peek == 39) {  // $' - suffix
         ++position;
         result += SubString(subject, matchInfo[CAPTURE1], subject.length);
+      } else if (peek >= 48 && peek <= 57) {  // between '0' and '9'
+        // Convert to digit by subtracting '0'.
+        var scaled_index;
+        var advance;
+        if (peek == 48) {  // $0...
+          if (position + 1 == string.length ||  // ends with '$0', invalid.
+              %_StringCharCodeAt(string, position + 1) != 49) {  // not '$01'

[ulan, 2013/02/05 09:30:58]

As discussed offline, we should check $02, ... $nn here too.

+            scaled_index = 1 << 18;
+          } else {
+            scaled_index = 2; // 1 * 2
+            advance = 2;
+          }
+        } else if (peek == 49 &&
+                   position + 1 < string.length &&
+                   %_StringCharCodeAt(string, position + 1) == 48) {  // $10
+          scaled_index = 20;  // 10 * 2
+          advance = 2;
+        } else {
+          scaled_index = (peek - 48) << 1;  // index * 2
+          advance = 1;
+        }
+
+        if (NUMBER_OF_CAPTURES(matchInfo) > scaled_index) {
+          var start = matchInfo[CAPTURE(scaled_index)];
+          if (start >= 0) {
+            result +=
+              SubString(subject, start, matchInfo[CAPTURE(scaled_index + 1)]);
+          }
+          position += advance;
+        } else {
+          result += '$';
+        }
       } else {
         result += '$';
       }