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

TBR=tebbi@chromium.org
BUG=chromium:668510

Review-Url: https://codereview.chromium.org/2526223003
Cr-Commit-Position: refs/heads/master@{#41280}

src/conversions.cc

@@ -474,12 +474,15 @@ char* DoubleToRadixCString(double value, int radix) {
     } 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.

test/mjsunit/number-tostring.js

@@ -151,6 +151,9 @@ assertEquals("10000", (81).toString(3));
 assertEquals("10000.01", (81 + 1/9).toString(3));
 assertEquals("0.0212010212010212010212010212010212", (2/7).toString(3));
 
+assertEquals("314404114120101444444424000000000000000",
+             (1.2345e+27).toString(5));
+
 // ----------------------------------------------------------------------
 // toFixed
 assertEquals("NaN", (NaN).toFixed(2));