Question

I have two bytes, 8 bit octets, which should be read as: [3 bits][4 bits][3 bits].

Example:

unsigned char octet1 = 0b11111111;  // binary values
unsigned char octet2 = 0b00000011;

As integers: [7][15][7].

Anybody can give me a hint where to start?

Answer 1

No need to put the two bytes together before extracting bits we want.

#include <stdio.h>

main()
{
    unsigned char octet1 = 0b11111111;
    unsigned char octet2 = 0b00000011;
    unsigned char n1 = octet1 & 0b111;
    unsigned char n2 = (octet1 >> 3) & 0b1111;
    unsigned char n3 = (octet1 >> 7) | (octet2 + octet2);

    printf("octet1=%u octet2=%u n1=%u n2=%u n3=%u\n",
              octet1, octet2, n1, n2, n3);

}