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Problem to convert array of bytes to array of bits

 
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karlosguay



Joined: 12 Jun 2013
Posts: 20

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Problem to convert array of bytes to array of bits
PostPosted: Wed Sep 11, 2013 2:08 am     Reply with quote

Buenos días:

Estoy intentando hacer un programa donde tengo 19 bytes en una cadena (int telemando1[19]) y los intento leer y meter en otra bit a bit (int1 telemandobits[152]). El objetivo es que si tengo en la primera cadena los valores 8,7,.... pasen a la segunda cadena con los valores binarios 0,0,0,0,1,0,0,0, 0,0,0,0,0,1,1,1, ...

El código que tengo es:

Code:

   int telemando1[19];
   int1 telemandobits[152];
   int i,z;

     for (i=0;i==151;i++) //Aqui inicializo la cadena
     {
         telemandobits[i]=0;
     }

        //Estos son los datos que quiero pasar a la otra cadena bit a bit
         telemando1[18]=8;
         telemando1[17]=7;
         telemando1[16]=6;
         telemando1[15]=5;
         telemando1[14]=4;
         telemando1[13]=12;
         telemando1[12]=0;
         telemando1[11]=1;
         telemando1[10]=17;
         telemando1[9]=255;
         telemando1[8]=255;
         telemando1[7]=255;
         telemando1[6]=255;
         telemando1[5]=255;
         telemando1[4]=255;
         telemando1[3]=255;
         telemando1[2]=255;
         telemando1[1]=0;
         telemando1[0]=0;

         //Aquí creo una cadena de bits con todos los datos
         for (i=18;i==0;i--)
         {  for (z=0;z==7;z++)
              { 
                 telemandobits[((i+1)*8)-(8-z)]=(int1) telemando1[i];
                 telemando1[i]>>=1; // x>>=y, is the same as x=x>>y
              }
         }


Luego leo la cadena telemandobits[] y no tengo los valores 0 y 1 esperados. La verdad es que creo que tiene que ser una tontería que no veo, pero me estoy volviendo loco. ConfusedConfused
Alguna sugerencia??

Gracias
alan



Joined: 12 Nov 2012
Posts: 357
Location: South Africa

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PostPosted: Wed Sep 11, 2013 2:11 am     Reply with quote

Format are as follow for for loop

Code:
for (i=0; i<= 151, i++) {


Regards
karlosguay



Joined: 12 Jun 2013
Posts: 20

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PostPosted: Wed Sep 11, 2013 2:16 am     Reply with quote

Sorry Alan, I don´t understand
karlosguay



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PostPosted: Wed Sep 11, 2013 2:33 am     Reply with quote

In English better

I need pass bytes in array "int telemando1[19]" to another array "int1 telemandobits[152]" bit to bit. If in the first array bytes are 8,7,6, ... I need in the second array 0,0,0,0,1,0,0,0, 0,0,0,0,0,1,1,1, 0,0,0,0,0,1,1,0, ....

Code:
  int telemando1[19];
   int1 telemandobits[152];
   int i,z;

     for (i=0;i==151;i++) //Aqui inicializo la cadena
     {
         telemandobits[i]=0;
     }

        //Estos son los datos que quiero pasar a la otra cadena bit a bit
         telemando1[18]=8;
         telemando1[17]=7;
         telemando1[16]=6;
         telemando1[15]=5;
         telemando1[14]=4;
         telemando1[13]=12;
         telemando1[12]=0;
         telemando1[11]=1;
         telemando1[10]=17;
         telemando1[9]=255;
         telemando1[8]=255;
         telemando1[7]=255;
         telemando1[6]=255;
         telemando1[5]=255;
         telemando1[4]=255;
         telemando1[3]=255;
         telemando1[2]=255;
         telemando1[1]=0;
         telemando1[0]=0;

         //Aquí creo una cadena de bits con todos los datos
         for (i=18;i==0;i--)
         {  for (z=0;z==7;z++)
              { 
                 telemandobits[((i+1)*8)-(8-z)]=(int1) telemando1[i];
                 telemando1[i]>>=1; // x>>=y, is the same as x=x>>y
              }
         }


But in "telemandobits" there are no correct values.
Any idea??

Thanks
alan



Joined: 12 Nov 2012
Posts: 357
Location: South Africa

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PostPosted: Wed Sep 11, 2013 2:40 am     Reply with quote

Yes your "for loop" never executes.

It set i = 0, then test if i == 152, and because it is not equal to 152 it exits the loop.

You have to test for i <= 152 and while this evaluates to TRUE, the for loop will execute. Sorry I am bad at explaining anything, but hope this helps.

Regards
karlosguay



Joined: 12 Jun 2013
Posts: 20

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PostPosted: Wed Sep 11, 2013 2:53 am     Reply with quote

OK Alan, you are a good teacher. Smile

regards
karlosguay



Joined: 12 Jun 2013
Posts: 20

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PostPosted: Wed Sep 11, 2013 3:05 am     Reply with quote

Now the code is

Code:
     for (i=0;i<=151;i++)
     {
         telemandobits[i]=0;
     }

         telemando1[18]=8;
         telemando1[17]=7;
         telemando1[16]=6;
         telemando1[15]=5;
         telemando1[14]=4;
         telemando1[13]=12;
         telemando1[12]=0;
         telemando1[11]=1;
         telemando1[10]=17;
         telemando1[9]=255;
         telemando1[8]=255;
         telemando1[7]=255;
         telemando1[6]=255;
         telemando1[5]=255;
         telemando1[4]=255;
         telemando1[3]=255;
         telemando1[2]=255;
         telemando1[1]=0;
         telemando1[0]=0;

         //Aquí creo una cadena de bits con todos los datos
         for (i=0;i<=18;i++)
         {  for (z=0;z<=7;z++)
            { 
               telemandobits[((i+1)*8)-(8-z)]=(int1) telemando1[i];
               telemando1[i]>>=1; // x>>=y, is the same as x=x>>y
            }
         }
   


But in "telemandobits" array i have 1,0,1,0,1,0,1,0,1,0,...
Ttelmah



Joined: 11 Mar 2010
Posts: 19515

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PostPosted: Wed Sep 11, 2013 3:34 am     Reply with quote

>>=1, multiplies the value by 2. To get the next bit into the low bit you need <<=1. Explicitly test the low bit (=telemando1[i] & 1;). No cast needed.

However this is all basically not needed. You can create a union between the bits and the bytes, and the bits will all be there, with no copying needed. Instantaneous, versus a lot of code....
Code:

   union {
      int telemando1[19];
      int1 telemandobits[152];
  } val;
   
  val.telemando1[18]=8;
  val.telemando1[17]=7;
  val.telemando1[16]=6;
  val.telemando1[15]=5;
  val.telemando1[14]=4;
  val.telemando1[13]=12;
  val.telemando1[12]=0;
  val.telemando1[11]=1;
  val.telemando1[10]=17;
  val.telemando1[9]=255;
  val.telemando1[8]=255;
  val.telemando1[7]=255;
  val.telemando1[6]=255;
  val.telemando1[5]=255;
  val.telemando1[4]=255;
  val.telemando1[3]=255;
  val.telemando1[2]=255;
  val.telemando1[1]=0;
  val.telemando1[0]=0;


Then val.telemandobits[0] to [152], will contain the bits.

Best Wishes
karlosguay



Joined: 12 Jun 2013
Posts: 20

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PostPosted: Wed Sep 11, 2013 3:47 am     Reply with quote

Many thanks.

Never used "union", i go to use it.
alan



Joined: 12 Nov 2012
Posts: 357
Location: South Africa

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PostPosted: Wed Sep 11, 2013 3:48 am     Reply with quote

Hi Tthelmah, haven't you got it mixed. shift right >> divide and shift left << multiplies.

Regards
Alan
karlosguay



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PostPosted: Wed Sep 11, 2013 4:15 am     Reply with quote

Using "union" runs ok.
then the code is better.

Code:
   union {
      int telemando1[19];
      int1 telemandobits[152];
         } val;
 
//     for (i=0;i<=151;i++)
//     {
//         telemandobits[i]=0;
//     }

         val.telemando1[18]=8;
         val.telemando1[17]=7;
         val.telemando1[16]=6;
         val.telemando1[15]=5;
         val.telemando1[14]=4;
         val.telemando1[13]=12;
         val.telemando1[12]=0;
         val.telemando1[11]=1;
         val.telemando1[10]=17;
         val.telemando1[9]=255;
         val.telemando1[8]=255;
         val.telemando1[7]=255;
         val.telemando1[6]=255;
         val.telemando1[5]=255;
         val.telemando1[4]=255;
         val.telemando1[3]=255;
         val.telemando1[2]=255;
         val.telemando1[1]=0;
         val.telemando1[0]=0;

         //Aquí creo una cadena de bits con todos los datos
//         for (i=0;i<=18;i++)
//         {  for (z=0;z<=7;z++)
//            { 
//               telemandobits[((i+1)*8)-(8-z)]=(int1) telemando1[i];
//               telemando1[i]>>=1; // x>>=y, is the same as x=x>>y
//            }
//         }
         


Many thanks to all
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