3ds Cart2 rom save remover

3ds_cart2_save_fix.cpp

#include <cstdio>
#include <cstdlib>
#include <iostream>

using byte = uint8_t;

int main(int argc, const char* argv[])
{
  if (argc == 2)
  {
    FILE* in = fopen(argv[1], "rb");
    
    if (!in)
    {
      std::cout << "Input file doesn't exist" << std::endl;
      return -1;
    }
    
    FILE* out = fopen("out.3ds", "wb");
    
    if (!out)
    {
      fclose(in);
      std::cout << "Unable to create output file" << std::endl;
      return -1;
    }
      
    
    constexpr size_t START_OFFSET = 0x77280000;
    constexpr size_t END_OFFSET = 0x80000000;
    constexpr size_t BUFFER_SIZE = 2 << 24; /* 16 MB */
    
    fseek(in, 0, SEEK_END);
    const size_t fileLength = ftell(in);
    fseek(in, 0, SEEK_SET);
    size_t position = 0;
    
    byte* buffer = new byte[BUFFER_SIZE];
    
    while (position < fileLength)
    {
      const size_t step = std::min((position < START_OFFSET ? START_OFFSET : fileLength) - position, BUFFER_SIZE);
      size_t check = 0;
      
      if (position < START_OFFSET)
        check = fread(buffer, 1, step, in);
      else if (position == START_OFFSET)
        std::fill(buffer, buffer + BUFFER_SIZE, 0xFF);
      
      if (check != step)
      {
        std::cout << "I/O read error" << std::endl;
        break;
      }
      
      check = fwrite(buffer, 1, step, out);
      
      if (check != step)
      {
        std::cout << "I/O read error" << std::endl;
        break;
      }
      else
        std::cout << "processed " << position << " bytes.." << std::endl;
      
      position += step;
    }
    
    delete [] buffer;
    fclose(in);
    fclose(out);
  }
  else
    std::cout << "Please specify an input file" << std::endl;
  
  return 0;
}