Improve array to string conversion.

src/runtime.cc

 // Copyright 2012 the V8 project authors. All rights reserved.
 // Redistribution and use in source and binary forms, with or without
 // modification, are permitted provided that the following conditions are
 // met:
 //
 //     * Redistributions of source code must retain the above copyright
 //       notice, this list of conditions and the following disclaimer.
 //     * Redistributions in binary form must reproduce the above
 //       copyright notice, this list of conditions and the following
 //       disclaimer in the documentation and/or other materials provided
@@ skipping 5045 matching lines @@
       return Smi::FromInt(d);
     }
   }
 
   // Slower case.
   return isolate->heap()->NumberFromDouble(
       StringToDouble(isolate->unicode_cache(), subject, ALLOW_HEX));
 }
 
 
-RUNTIME_FUNCTION(MaybeObject*, Runtime_StringFromCharCodeArray) {
-  NoHandleAllocation ha;
-  ASSERT(args.length() == 1);
-
-  CONVERT_ARG_CHECKED(JSArray, codes, 0);
-  int length = Smi::cast(codes->length())->value();
-
-  // Check if the string can be ASCII.
-  int i;
-  for (i = 0; i < length; i++) {
-    Object* element;
-    { MaybeObject* maybe_element = codes->GetElement(i);
-      // We probably can't get an exception here, but just in order to enforce
-      // the checking of inputs in the runtime calls we check here.
-      if (!maybe_element->ToObject(&element)) return maybe_element;
-    }
-    CONVERT_NUMBER_CHECKED(int, chr, Int32, element);
-    if ((chr & 0xffff) > String::kMaxAsciiCharCode)
-      break;
+RUNTIME_FUNCTION(MaybeObject*, Runtime_NewString) {
+  CONVERT_SMI_ARG_CHECKED(length, 0);
+  CONVERT_BOOLEAN_ARG_CHECKED(is_one_byte, 1);
+  if (length == 0) return isolate->heap()->empty_string();
+  if (is_one_byte) {
+    return isolate->heap()->AllocateRawOneByteString(length);
+  } else {
+    return isolate->heap()->AllocateRawTwoByteString(length);
   }
-
-  MaybeObject* maybe_object = NULL;
-  if (i == length) {  // The string is ASCII.
-    maybe_object = isolate->heap()->AllocateRawOneByteString(length);
-  } else {  // The string is not ASCII.
-    maybe_object = isolate->heap()->AllocateRawTwoByteString(length);
-  }
-
-  Object* object = NULL;
-  if (!maybe_object->ToObject(&object)) return maybe_object;
-  String* result = String::cast(object);
-  for (int i = 0; i < length; i++) {
-    Object* element;
-    { MaybeObject* maybe_element = codes->GetElement(i);
-      if (!maybe_element->ToObject(&element)) return maybe_element;
-    }
-    CONVERT_NUMBER_CHECKED(int, chr, Int32, element);
-    result->Set(i, chr & 0xffff);
-  }
-  return result;
 }
 
 
+RUNTIME_FUNCTION(MaybeObject*, Runtime_TruncateString) {
+  CONVERT_ARG_CHECKED(SeqString, string, 0);
+  CONVERT_SMI_ARG_CHECKED(new_length, 1);
+  RUNTIME_ASSERT(new_length <= string->length());
+  RUNTIME_ASSERT(new_length > 0);
+  if (new_length != string->length()) string->Truncate(new_length);
+  return string;
+}
+
+
 // kNotEscaped is generated by the following:
 //
 // #!/bin/perl
 // for (my $i = 0; $i < 256; $i++) {
 //   print "\n" if $i % 16 == 0;
 //   my $c = chr($i);
 //   my $escaped = 1;
 //   $escaped = 0 if $c =~ m#[A-Za-z0-9@*_+./-]#;
 //   print $escaped ? "0, " : "1, ";
 // }
@@ skipping 8264 matching lines @@
     // Handle last resort GC and make sure to allow future allocations
     // to grow the heap without causing GCs (if possible).
     isolate->counters()->gc_last_resort_from_js()->Increment();
     isolate->heap()->CollectAllGarbage(Heap::kNoGCFlags,
                                        "Runtime::PerformGC");
   }
 }
 
 
 } }  // namespace v8::internal