[Merge to M56] Verify precision length before converting to string.

fpdfsdk/javascript/PublicMethods.cpp

 // Copyright 2014 PDFium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 // Original code copyright 2014 Foxit Software Inc. http://www.foxitsoftware.com
 
 #include "fpdfsdk/javascript/PublicMethods.h"
 
 #include <algorithm>
 #include <iomanip>
+#include <limits>
 #include <sstream>
 #include <string>
 #include <vector>
 
 #include "core/fpdfdoc/cpdf_interform.h"
 #include "core/fxcrt/fx_ext.h"
 #include "fpdfsdk/cpdfsdk_formfillenvironment.h"
 #include "fpdfsdk/cpdfsdk_interform.h"
 #include "fpdfsdk/javascript/Field.h"
 #include "fpdfsdk/javascript/JS_Define.h"
@@ skipping 67 matching lines @@
 }
 
 #if _FX_OS_ != _FX_ANDROID_
 CFX_ByteString CalculateString(double dValue,
                                int iDec,
                                int* iDec2,
                                bool* bNegative) {
   *bNegative = dValue < 0;
   if (*bNegative)
     dValue = -dValue;
+
+  // Make sure the number of precision characters will fit.
+  if (iDec > std::numeric_limits<double>::digits10)
+    iDec = std::numeric_limits<double>::digits10;
+
   std::stringstream ss;
   ss << std::fixed << std::setprecision(iDec) << dValue;
   std::string stringValue = ss.str();
   size_t iDecimalPos = stringValue.find(".");
   *iDec2 = iDecimalPos == std::string::npos ? stringValue.size()
                                             : static_cast<int>(iDecimalPos);
   return CFX_ByteString(stringValue.c_str());
 }
 #endif
 
@@ skipping 1705 matching lines @@
     nums.SetElement(pRuntime, nIndex, CJS_Value(pRuntime, sPart.c_str()));
   }
 
   if (nums.GetLength(pRuntime) > 0)
     vRet = CJS_Value(pRuntime, nums);
   else
     vRet.SetNull(pRuntime);
 
   return true;
 }