Flips a surface in SDL

gistfile1.cpp

SDL_Surface* flip_vertical(SDL_Surface* sfc) {
     SDL_Surface* result = SDL_CreateRGBSurface(sfc->flags, sfc->w, sfc->h,
         sfc->format->BytesPerPixel * 8, sfc->format->Rmask, sfc->format->Gmask,
         sfc->format->Bmask, sfc->format->Amask);
     const auto pitch = sfc->pitch;
     const auto pxlength = pitch*(sfc->h - 1);
     auto pixels = static_cast<unsigned char*>(sfc->pixels) + pxlength;
     auto rpixels = static_cast<unsigned char*>(result->pixels) ;
     for(auto line = 0; line < sfc->h; ++line) {
         memcpy(rpixels,pixels,pitch);
         pixels -= pitch;
         rpixels += pitch;
     }
     return result;
}

How would I approach doing this operation but for horizontal flipping