Fix Number.prototype.toString with non-default radix wrt modulo.

src/conversions.cc

 // Copyright 2011 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/conversions.h"
 
 #include <limits.h>
 #include <stdarg.h>
 #include <cmath>
 
@@ skipping 456 matching lines @@
               buffer[fraction_cursor++] = chars[digit + 1];
               break;
             }
           }
           break;
         }
       }
     } while (fraction > delta);
   }
 
-  // Compute integer digits.
+  // Compute integer digits. Fill unrepresented digits with zero.
+  while (Double(integer / radix).Exponent() > 0) {
+    integer /= radix;
+    buffer[--integer_cursor] = '0';
+  }
   do {
-    double multiple = std::floor(integer / radix);
-    int digit = static_cast<int>(integer - multiple * radix);
-    buffer[--integer_cursor] = chars[digit];
-    integer = multiple;
+    double remainder = modulo(integer, radix);
+    buffer[--integer_cursor] = chars[static_cast<int>(remainder)];
+    integer = (integer - remainder) / radix;
   } while (integer > 0);
 
   // Add sign and terminate string.
   if (negative) buffer[--integer_cursor] = '-';
   buffer[fraction_cursor++] = '\0';
   // Allocate new string as return value.
   char* result = NewArray<char>(fraction_cursor - integer_cursor);
   memcpy(result, buffer + integer_cursor, fraction_cursor - integer_cursor);
   return result;
 }
@@ skipping 70 matching lines @@
   char reverse_buffer[kBufferSize + 1];  // Result will be /0 terminated.
   Vector<char> reverse_vector(reverse_buffer, arraysize(reverse_buffer));
   const char* reverse_string = DoubleToCString(d, reverse_vector);
   for (int i = 0; i < length; ++i) {
     if (static_cast<uint16_t>(reverse_string[i]) != buffer[i]) return false;
   }
   return true;
 }
 }  // namespace internal
 }  // namespace v8