Need Advice from C Gurus

Comments

• davidsaunders Posts: 1,559

  March 2017

  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: 1,372

  March 2017 edited March 2017

  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: 4,586

  March 2017

  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

  March 2017 edited March 2017

  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: 4,586

  March 2017

  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: 866

  March 2017 edited March 2017

  Eric,
  What is the link to the spin2cpp programs?
  
  Thanks
  Tom
• ersmith Posts: 4,586

  March 2017

  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: 76

  March 2017

  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: 2,916

  March 2017

  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

  March 2017

  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: 21,233

  March 2017

  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 ?