// Automatically generated C++ file on Wed Mar 27 09:18:19 2024
//
// To build with Digital Mars C++ Compiler:
//
//    dmc -mn -WD derivativedll.cpp kernel32.lib

#include <malloc.h>

union uData
{
   bool b;
   char c;
   unsigned char uc;
   short s;
   unsigned short us;
   int i;
   unsigned int ui;
   float f;
   double d;
   long long int i64;
   unsigned long long int ui64;
   char *str;
   unsigned char *bytes;
};

// int DllMain() must exist and return 1 for a process to load the .DLL
// See https://docs.microsoft.com/en-us/windows/win32/dlls/dllmain for more information.
int __stdcall DllMain(void *module, unsigned int reason, void *reserved) { return 1; }

void bzero(void *ptr, unsigned int count)
{
   unsigned char *first = (unsigned char *) ptr;
   unsigned char *last  = first + count;
   while(first < last)
      *first++ = '\0';
}

// #undef pin names lest they collide with names in any header file(s) you might include.
#undef x
#undef dx

struct sDERIVATIVEDLL
{
  // declare the structure here
  double lastT;
  double lastx;
};

extern "C" __declspec(dllexport) void derivativedll(struct sDERIVATIVEDLL **opaque, double t, union uData *data)
{
   double  x  = data[0].d; // input
   double &dx = data[1].d; // output

   if(!*opaque)
   {
      *opaque = (struct sDERIVATIVEDLL *) malloc(sizeof(struct sDERIVATIVEDLL));
      bzero(*opaque, sizeof(struct sDERIVATIVEDLL));
   }
   struct sDERIVATIVEDLL *inst = *opaque;

// Implement module evaluation code here:
   double Ts = t - inst->lastT;
   dx = (x - inst->lastx)/Ts;
   inst->lastT = t;
   inst->lastx = x;
}

extern "C" __declspec(dllexport) void Destroy(struct sDERIVATIVEDLL *inst)
{
   free(inst);
}