CODEWITHSUNDEEP
c
user2989964
user2989964

Reputation: 131

Splitting 3 bytes into six 4 bits and recombining to two 12 bits

I'm trying to figure out a way to split a byte into two (eg. F8 to F and 8) to be later recombined with other bytes. I read up on bit masking but I still don't quite understand it. This is what I'm trying to do.

F8 FF FF - Split the bytes into two. I'll use variables to distinguish the bytes

u=F, v=8, w=F, x=F, y=F, z=F, which are essentially, uv, wx, yz

The end result would be FF8 FFF or in variables, xuv yzw.

Does anyone know how to do this? Thanks in advance!

Upvotes: 0

Views: 1065

Answers (2)

Frerich Raabe
Frerich Raabe

Reputation: 94409

If you aren't too familiar with logical operators, I suggest to introduce two little helper functions to encapsulate this stuff:

void split_nibbles( unsigned char ch, unsigned char *higherOrder, unsighed char *lowerOrder )
{
  *higherOrder = ch >> 4;
  *lowerOrder = ch & 0x0f;
}

 unsigned char merge_nibbles( unsigned char higherOrder, unsigned char lowerOrder )
 {
   return (higherOrder << 4) | (lowerOrder & 0x0f);
 }

You can then write

unsigned char bytes[] = { 0xf8, 0xff, 0xff };

unsigned char u, v, w, x, y, z;
split_nibbles( bytes[0], &u, &v );
split_nibbles( bytes[1], &w, &x );
split_nibbles( bytes[2], &y, &z );

bytes[0] = merge_nibbles( x, u );
bytes[1] = merge_nibbles( v, y );
bytes[2] = merge_nibbles( z, w );

...which is very close to your description. :-)

Upvotes: 1

Nathan Fellman
Nathan Fellman

Reputation: 127538

If you have a variable x with a value known to fit into one byte, you can split it into two nibbles like this:

x_lo = x & 0xf;
x_hi = (x >> 4) & 0xf;

To combine two nibbles y_lo and y_hi into one byte you shift and or:

y = y_lo | (y_hi << 4);

Upvotes: 2

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