Make smi.toString() do its work faster using native string helpers.

runtime/lib/integers.cc

 // Copyright (c) 2012, the Dart project authors.  Please see the AUTHORS file
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
 #include "vm/bootstrap_natives.h"
 
 #include "vm/bigint_operations.h"
 #include "vm/dart_entry.h"
 #include "vm/exceptions.h"
 #include "vm/native_entry.h"
@@ skipping 326 matching lines @@
   const Smi& operand = Smi::CheckedHandle(arguments->NativeArgAt(0));
   if (FLAG_trace_intrinsified_natives) {
     OS::Print("Smi_bitLength: %s\n", operand.ToCString());
   }
   int64_t value = operand.AsInt64Value();
   intptr_t result = BitLengthInt64(value);
   ASSERT(Smi::IsValid(result));
   return Smi::New(result);
 }
 
+DEFINE_NATIVE_ENTRY(Smi_toString, 1) {
+  const Smi& operand = Smi::CheckedHandle(arguments->NativeArgAt(0));
+  if (FLAG_trace_intrinsified_natives) {
+    OS::Print("Smi_toString: %s\n", operand.ToCString());
+  }
+  // Maximal number of digits of a 63 bit number is 19. Add one for minus sign.

[Lasse Reichstein Nielsen, 2013/09/23 11:25:18]

I decided against using OS::SNPrint(characters, 0, "%ld", signed_value) because
I assume it will have some kind of overhead in parsing the format.
We should try that too, and see what's faster.

And I should make some timings of this change as well.

+  const size_t kMaxLength = 20;
+  uint8_t characters[kMaxLength];
+  uint8_t* end = characters + kMaxLength;
+  uint8_t* cursor = end;
+  bool negative = false;
+  int64_t signed_value = operand.AsInt64Value();
+  uint64_t value;
+  if (signed_value < 0) {
+    negative = true;
+    value = -signed_value;
+  } else {
+    value = signed_value;
+  }
+  do {
+    uint64_t digit = value % 10;
+    value = (value - digit) / 10;
+    *--cursor = '0' + digit;
+  } while (value);
+  if (negative) {
+    *--cursor = '-';
+  }
+  intptr_t length = static_cast<intptr_t>(end - cursor);
+  return OneByteString::New(cursor, length, Heap::kNew);
+}
+
 
 // Mint natives.
 
 DEFINE_NATIVE_ENTRY(Mint_bitNegate, 1) {
   const Mint& operand = Mint::CheckedHandle(arguments->NativeArgAt(0));
   ASSERT(CheckInteger(operand));
   if (FLAG_trace_intrinsified_natives) {
     OS::Print("Mint_bitNegate: %s\n", operand.ToCString());
   }
   int64_t result = ~operand.value();
@@ skipping 46 matching lines @@
   // Use the preallocated out of memory exception to avoid calling
   // into dart code or allocating any code.
   const Instance& exception =
       Instance::Handle(isolate->object_store()->out_of_memory());
   Exceptions::Throw(exception);
   UNREACHABLE();
   return 0;
 }
 
 }  // namespace dart