Patch for bug open-source-parsers#53 on version 0.5.0

This is a patch that we have utilized at IDEXX Labs for the the bug described above.
We have tested and verified this on x86 32 and 64 bit linux and 32 bit arm.

Author: hiharin

src/lib_json/json_writer.cpp

@@ -13,6 +13,7 @@
 #include <string.h>
 #include <sstream>
 #include <iomanip>
+#include <math.h>
 
 #if defined(_MSC_VER) && _MSC_VER >= 1400 // VC++ 8.0
 // Disable warning about strdup being deprecated.
@@ -79,7 +80,29 @@ std::string valueToString(double value) {
   sprintf_s(buffer, sizeof(buffer), "%.16g", value);
   #endif
 #else
-  snprintf(buffer, sizeof(buffer), "%.16g", value);
+  if ( isfinite( value ))
+  {
+     snprintf(buffer, sizeof(buffer), "%.16g", value);
+  }
+  else
+  {
+     // IEEE standard states that NaN values will not compare to themselves
+     if ( value != value)
+     {
+        snprintf(buffer, sizeof(buffer), "null");
+     }
+     else if ( value < 0)
+     {
+        snprintf(buffer, sizeof(buffer), "-1e+9999");
+     }
+     else
+     {
+        snprintf(buffer, sizeof(buffer), "1e+9999");
+     }
+     // nothing more to do, return.
+     return buffer;
+  }
+
 #endif
   fixNumericLocale(buffer, buffer + strlen(buffer));
   return buffer;