typedef byte * pbyte;

// mask arrays
byte bulletmask[1][3][3];
byte plmask[24][64][64];
byte a1mask[24][280][280];
byte a2mask[24][140][140];
byte a3mask[24][70][70];
byte a4mask[24][35][35];
byte alienmask[64][64];

pbyte GetMask(int type, int rotation, int size) {
  switch (type) {
    case tAsteroid: // asteroid
      {
        switch (size)
          {
            case 280:
              return (pbyte)&a1mask[rotation];
            case 140:
              return (pbyte)&a2mask[rotation];
            case 70:
              return (pbyte)&a3mask[rotation];
            case 35:
              return (pbyte)&a4mask[rotation];
          }
      };
    case tBullet: // bullet
      return (pbyte)&bulletmask;
    case tPlayer: // player
      return (pbyte)&plmask[rotation];
    case tAlien:
      return (pbyte)&alienmask;
    } 
  return 0; // null - should never get here!
}

In my post about collision detection I mentioned getting mask bytes. This function GetMask returns a pointer to a byte (i.e. the first byte in a particular mask for a particular type of object (asteroid, bullet, player, alien) and for asteroids and the player a particular rotation. The many (pbyte) are needed because the arrays have different sizes. There are 24 player and asteroid masks.