Need Advice from C Gurus

Comments

• davidsaunders Posts: 1,559

  2017-03-13 18:24

  I have done little with C on the prop.
  
  Though if you compile your program as COG only is it not possible to just index from a pointer passed in PAR?
• dgately Posts: 1,641

  2017-03-13 18:35 edited 2017-03-13 18:35

  I let spin2cpp do the work. Possibly the convert from longfill to memset is not obvious when translating from Spin to C...
  

  spin2cpp --ccode test.spin
  

  void test_play_music()
  {
    int32_t   nfreq;
    if (p_music <= 0) {                    // manual stop invoked?                                               
      test_freq_out(0, TEST_SPKR, 0);
      return;
    }
  
    if ((--nmillis) > 0) {                 // is note playing now?                                                        
      return;
    }
                                                                
    nfreq = ((int32_t *)p_music)[0];       // get note
    p_music = p_music + 4;                 // advance to timing
    if (nfreq < 0) {                       // if end                                           
      memset( (void *)(&p_music), 0, sizeof(int32_t)*2);
      return;
    }
                                                                
    nmillis = (((int32_t *)p_music)[0] * 60) / ((int32_t *)&dat[0])[0];       // adjust timing for bpm
    p_music = p_music + 4;                                                    // start the note
    test_freq_out(0, TEST_SPKR, nfreq);
  }
  

  
  
  dgately
• ersmith Posts: 6,226

  2017-03-13 18:42

  It looks like p_music wants to be a pointer to integers, so you would have something like:

  int Charge[] = {
     N_G3, T_8TH, N_C4,
     /* and so on... */
  };
  int *p_music;
  
  void play_music() {
     n_freq = *p_music++;
     nmillisec = (*p_music++) * 60 / BPM;
     freq_out(0, SPKR, n_freq);
  }
  /* somewhere in initialization */
  p_music = Charge;
  

  C's handling of pointer accesses is very much like Spin's, except that C pointers are typed so "++" advances to the next element rather than the next byte (so you just do "p_music++" rather than "p_music += 4").
  
  
• JasonDorie Posts: 1,930

  2017-03-13 18:47 edited 2017-03-13 18:48

  In C/C++, if you declare an array of something, you can pass the pointer by simply passing the name of the array, instead of passing a specific element, like this:
  

  void PrintArray( long * ptrToNumbers )   // long * means "pointer to a long"
  {
    int index = 0;
    while( ptrToNumbers[index] != -1 )
    {
      // printf is "print formatted", and %d means "decimal number" - it will be
      // replaced by one of the arguments after the quoted string
      printf( "Number at index %d is : %d\n", index, ptrToNumbers[index] );
      index += 1;
    }
  }
  
  void main(void)
  {
    // declare the array with contents, -1 is the terminating element so you don't have to pass the size
    long MyArray[] = {5, 6, 7, 8, 9, 10, -1};
  
    // pass the pointer to the array to the printing function
    PrintArray( MyArray );
  }
  
• ersmith Posts: 6,226

  2017-03-13 18:48

  And yes, spin2cpp is useful for this kind of thing. You can use the spincvt GUI if you don't like command lines. Select "C Output" under options, then File > Open Spin File and select your .spin file. The Spin code will be loaded in the left hand pane, and the converted C code will appear on the right hand pane (with the command line used to do the conversion printed on the bottom).
  
• twm47099 Posts: 867

  2017-03-13 19:27 edited 2017-03-13 19:28

  Eric,
  What is the link to the spin2cpp programs?
  
  Thanks
  Tom
• ersmith Posts: 6,226

  2017-03-13 19:38

  twm47099 wrote: »

  Eric,
  What is the link to the spin2cpp programs?
  
  Thanks
  Tom

  
  The source code is at https://github.com/totalspectrum/spin2cpp/.
  There are binary releases here.
  
  
  
• laurent974 Posts: 77

  2017-03-13 20:04

  i'm not a C guru but i found that book really good to brush up my rusty C and catch up with C99 standard.
  21st Century C
  
  For instance to initialize a structure :
  
  MY_TYPE a = { .flag = true, .value = 123, .stuff = 0.456 }; (from a stack overflow answer but the book describes this more accurately)
  Other members are initialized as zero
• DavidZemon Posts: 2,973

  2017-03-13 21:20

  laurent974 wrote: »

  For instance to initialize a structure :
  
  MY_TYPE a = { .flag = true, .value = 123, .stuff = 0.456 };

  
  That's new syntax for me! Thanks for sharing
• davidsaunders Posts: 1,559

  2017-03-13 23:41

  laurent974 wrote: »

  i'm not a C guru but i found that book really good to brush up my rusty C and catch up with C99 standard.
  21st Century C
  
  For instance to initialize a structure :
  
  MY_TYPE a = { .flag = true, .value = 123, .stuff = 0.456 }; (from a stack overflow answer but the book describes this more accurately)
  Other members are initialized as zero

  Wow that is a rather verbose syntax. Did not know that was possible, thank you.
  
  I really need to see about C on the Propeller, seeing some of the examples there would be very little change between C code for WiringPi on the Raspberry Pi and code for the Propeller in many cases, this could definitely make for some interesting possibilities.
  
• Heater. Posts: 21,230

  2017-03-14 05:23

  How is that verbose syntax? It's about the same as doing a similar job is many other languages.
  
  E.g Javascript:
  
  let a = {flag : true, value : 123, stuff : 0.456};
  
  Or Python:
  
  a = {'flag': True, 'value': 123, 'stuff': 0.456}
  
  What language does it more concisely ?