During StringToDouble negative exponents may be less than -999 with a result ...

src/conversions.cc

 // Copyright 2006-2008 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 647 matching lines @@
   const int kMaxDigitsInInt = 9 * sizeof(int) / 4;  // NOLINT
 
   if (exponent != 0) {
     ASSERT(buffer_pos < kBufferSize);
     buffer[buffer_pos++] = 'e';
     if (exponent < 0) {
       ASSERT(buffer_pos < kBufferSize);
       buffer[buffer_pos++] = '-';
       exponent = -exponent;
     }
-    if (exponent > 999) exponent = 999;  // Result will be Infinity or 0 or -0.
 
-    const int exp_digits = 3;
+    // The minimal/maximal double is +/-1.7e-308. Given that
+    // the buffer contains at most 773 (kMaxSignificantDigits + 1) the
+    // minimal possible exponent is hence -(308 + 773)=-1081.
+    // Since leading zeros are removed the maximal exponent cannot exceed 308.
+    // If the following test triggers the result will be +/-infinity or +/-0.
+    if (exponent > 9999) exponent = 9999;
+
+    const int exp_digits = 4;
     for (int i = 0; i < exp_digits; i++) {
       buffer[buffer_pos + exp_digits - 1 - i] = '0' + exponent % 10;
       exponent /= 10;
     }
     ASSERT(exponent == 0);
     buffer_pos += exp_digits;
   } else if (!fractional_part && significant_digits <= kMaxDigitsInInt) {
     if (significant_digits == 0) return SignedZero(sign);
     ASSERT(buffer_pos > 0);
     int num = 0;
@@ skipping 484 matching lines @@
   // Allocate result and fill in the parts.
   StringBuilder builder(result_size + 1);
   builder.AddSubstring(integer_buffer + integer_pos + 1, integer_part_size);
   if (decimal_pos > 0) builder.AddCharacter('.');
   builder.AddSubstring(decimal_buffer, decimal_pos);
   return builder.Finalize();
 }
 
 
 } }  // namespace v8::internal