title: How do you do forward declarations in arduino code?
body: <p>I am trying to compile the polargraph code for arduino that someone else wrote. As far as I know the code itself is correct and after I add in the libraries needed to run it I get this error message.</p>
  
  <blockquote>
    <p>polargraph_server_polarshield.ino:109:16: error: 'prog_uint32_t' does not name a type<br/>
        In file included from /Applications/Arduino.app/Contents/Resources/Java/hardware/arduino/avr/cores/arduino/Arduino.h:28:0,
                         from /Applications/Arduino.app/Contents/Resources/Java/hardware/arduino/avr/libraries/SPI/SPI.h:17,
        from polargraph_server_polarshield.ino:47:<br/>
        util.ino: In function 'long unsigned int crc_update(long unsigned int, byte)':<br/>
        util.ino:392:31: error: 'crc_table' was not declared in this scope<br/>
        util.ino:394:31: error: 'crc_table' was not declared in this scope<br/>
        Error compiling.<br/></p>
  </blockquote>
  
  <p>I have heard that you need to set up a forward declaration because it uses two words in its data type and the official arduino compiler doesn't handle that well.  How do I go bout doing that?</p>