How do I rotate a sprite around a pivot point using SDL_gfx's rotozoomSurface?

Question

Using SDL_gfx's rotozoomSurface function to rotate a 38x58 sprite....naturally when it rotates it creates a new surface with a new size, and the rotation isn't going around the center point. I am actually having issues trying to figure out how to make it seem like its spinning around an axis...

Here is the image that I am using:

And here is the code that I have thus far:

  #define ANGLE_STEPS 32
  #define ANGLE_STEP  (360 / ANGLE_STEPS)
  ...
  int angle = 0;
  SDL_Rect cpos;
  cpos.x = cpos.y = 100;
  ...
  // create chopper angled surfaces
  for (int i = 0; i < ANGLE_STEPS; i++)
  {
    choppers[i] = rotozoomSurface(chopper, i * ANGLE_STEP, 1, 0);
  }
  ...

  // blit the currently requested angle
  SDL_BlitSurface(choppers[angle], NULL, screen, &cpos);
  ...

  // handle rotating the chopper
  if (keystate[keys[LEFTKEY]])
  {
    angle = (angle + 1) & (ANGLE_STEPS - 1);
    cpos.x = ?
    cpos.y = ?
  }
  if (keystate[keys[RIGHTKEY]])
  {
    angle = (angle - 1) & (ANGLE_STEPS - 1);
    cpos.x = ?
    cpos.y = ?
  }

Answer 1

Never mind, figured it out after simply sketching it out.

I calculated the center point of both the old and new sprite to be drawn, and simply subtracted that offset from the x and y points to be drawn.