ToString() causing hardfault

[josesimoes]

Details about Problem

nanoFramework area (Hardware/target board )

Detailed repro steps so we can see the same problem

1. The following code causes a hard fault on STM32
   ((long)-1234567899876543210).ToString("X16")

[sharmavishnu]

Additional Information

Performed a few tests on .NET Core 2.0 and nanoFramework. (This test was performed on build using files from repo on 9-Oct-18 and tried on STM32F401RE Nucleo board). Here are the results. See if this helps:

Test 1
.NET Core 2.0
long test = 32769;
string asStr = test.ToString("X7");
//String returned is 0x0008001 -- Correct

nanoFramework
long test = 32769;
string asStr = test.ToString("X7");
//String returned is 0x8001000 -- Incorrect

Test 2
.NET Core 2.0
long test = 64435;
string asStr = test.ToString("X8");
//String returned is 0x0000FBB3 -- Correct

nanoFramework
long test = 32769;
string asStr = test.ToString("X8");
//String returned is 0xFBB30000 -- Incorrect

Test 3
.NET Core 2.0
long test = 4294967294;
string asStr = test.ToString("X8");
//String returned is 0xFFFFFFFE -- Correct

nanoFramework
long test = 4294967294;
string asStr = test.ToString("X8");
//String returned is 0xFFFFFFFE -- Correct

Test 4
.NET Core 2.0
long test = 4294967294;
string asStr = test.ToString("X9");
//String returned is 0x0FFFFFFFE -- Correct

nanoFramework
long test = 4294967294;
string asStr = test.ToString("X9");
//String returned is 0xFFFFFFFE0 -- Incorrect

Test 5
.NET Core 2.0
long test = 4294967294;
string asStr = test.ToString("X10");
//String returned is 0x00FFFFFFFE -- Correct

nanoFramework
long test = 4294967294;
string asStr = test.ToString("X10");
//Debugger hangs...causes hardfault. Only way to recover is to re-flash hex files