Reimplement Number.prototype.toString with non-default radix.

src/builtins/builtins-number.cc

 // Copyright 2016 the V8 project authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #include "src/builtins/builtins-utils.h"
 #include "src/builtins/builtins.h"
 #include "src/code-factory.h"
 
 namespace v8 {
 namespace internal {
@@ skipping 527 matching lines @@
   // If {radix} is 10, just return ToString of {value}.
   if (radix_number == 10.0) return *isolate->factory()->NumberToString(value);
 
   // Make sure the {radix} is within the valid range.
   if (radix_number < 2.0 || radix_number > 36.0) {
     THROW_NEW_ERROR_RETURN_FAILURE(
         isolate, NewRangeError(MessageTemplate::kToRadixFormatRange));
   }
 
   // Fast case where the result is a one character string.
-  if (IsUint32Double(value_number) && value_number < radix_number) {
+  if ((IsUint32Double(value_number) && value_number < radix_number) ||
+      value_number == 0.0) {

[Tobias Tebbi, 2016/11/22 18:46:54]

nit: value_number == -0.0

     // Character array used for conversion.
     static const char kCharTable[] = "0123456789abcdefghijklmnopqrstuvwxyz";
     return *isolate->factory()->LookupSingleCharacterStringFromCode(
         kCharTable[static_cast<uint32_t>(value_number)]);
   }
 
   // Slow case.
   if (std::isnan(value_number)) return isolate->heap()->nan_string();
   if (std::isinf(value_number)) {
     return (value_number < 0.0) ? isolate->heap()->minus_infinity_string()
@@ skipping 1266 matching lines @@
   compiler::Node* lhs = assembler.Parameter(0);
   compiler::Node* rhs = assembler.Parameter(1);
   compiler::Node* context = assembler.Parameter(2);
 
   assembler.Return(assembler.StrictEqual(CodeStubAssembler::kNegateResult, lhs,
                                          rhs, context));
 }
 
 }  // namespace internal
 }  // namespace v8