Question

Language: C

Write a function unsigned char tvect(unsigned char v) that accepts an unsigned byte value and returns a transitioned byte with the following properties.

• bit7 = bit2 XOR bit3 /* That is, bit7 in the return byte is equal to bit2 in v xor’d with bit3 in v */

• bit6

• bit5

• bit4

• bit3

• bit2 bit7

• bit1

• bit0

= bit0
= bit1 OR bit2
= bit4 AND bit7 AND (NOT bit0)
= NOT bit5
= bit0 XOR bit1 XOR bit2 XOR bit3 XOR bit4 XOR bit5 XOR bit6 XOR

= bit1 AND bit2 = bit5 OR bit6

Answer 1

The question formatting is illegible so I am assuming this is the question asked.

• bit7 = bit2 XOR bit3

• bit6 = bit0

• bit5 = bit1 OR bit2

• bit4 = bit4 AND bit7 AND (NOT bit0)

• bit3 = NOT bit5

• bit2 = bit0 XOR bit1 XOR bit2 XOR bit3 XOR bit4 XOR bit5 XOR bit6 XOR bit7

• bit1 = bit1 AND bit2

• bit0 = bit5 OR bit6

Program:

unsigned char pow2[8] = {1, 2, 4, 8, 16, 32, 64, 128}; //storing powers of 2

int ISSET(unsigned char v, int i) //the ith bit can be extracted by v AND 2^i i.e. v & pow2[i]
{
    return (v & pow2[i]) != 0;
}

void SET(unsigned char *v, int i) //ith bit can be set by v OR 2^i i.e. v | pow2[i]
{
    *v = *v | pow2[i];
}

unsigned char tvect(unsigned char v)
{
    unsigned char ret = 0;
    if(ISSET(v, 2) ^ ISSET(v, 3)) //condtion for 7th bit
        SET(&ret, 7);
    if(ISSET(v, 0)) //condtion for 6th bit
        SET(&ret, 6);
    if(ISSET(v, 1) || ISSET(v, 2)) //condtion for 5th bit
        SET(&ret, 5);
    if(ISSET(v, 4) && ISSET(v, 7) && !ISSET(v, 0)) //condtion for 4th bit
        SET(&ret, 4);
    if(!ISSET(v, 5)) //condtion for 3rd bit
        SET(&ret, 3);
    //condtion for 2nd bit
    if(ISSET(v, 0) ^ ISSET(v, 1) ^ ISSET(v, 2) ^ ISSET(v, 3) ^ ISSET(v, 4) ^ ISSET(v, 5) ^ ISSET(v, 6) ^ ISSET(v, 7))
        SET(&ret, 2);
    if(ISSET(v, 1) && ISSET(v, 2)) //condtion for 1st bit
        SET(&ret, 1);
    if(ISSET(v, 5) || ISSET(v, 6)) //condtion for 0th bit
        SET(&ret, 0);
    return ret;
}