CODEWITHSUNDEEP
cbinary
daniel
daniel

Reputation: 15

Working with bits-output in c

I have to say what the output of the program for w = 33. I do not know how to do it. Does anyone have an idea how to solve this without writing the binary representation of each number?

void notChicken(int w) 
{
    unsigned int v1 = 0x12345678;
    unsigned int v2 = 0x87654785;
    unsigned int v3 = 0xffffffff;
    unsigned int tmp;
    tmp = (v1 >> 3) | (v2 << 3);
    tmp &= v3 & ~(v3 << (w >> 1));
    printf("%8x\n", tmp);
}

Thanks

Upvotes: 0

Views: 73

Answers (1)

Ajay Brahmakshatriya
Ajay Brahmakshatriya

Reputation: 9213

Although not a good idea, lets try to break down your operation.

You have given w = 33

The last part -

v3 & ~(v3 << (w >> 1)) is going to evaluate as v3 & ~(v3 << 16)

v3 << 16 is 0xffff0000 and ~ of that is 0xffff

since v3 is all ones you get 0xffff. This will mask off the upper 16 bits of the previous computation.

Now (v1 >> 3) | (v2 << 3);

We care only about the lower 16 bits.

>> 3 is dividing by 8 and << 3 is multiplying by 8.

So the result of first part will be

0x2468ACF | 0x3B2A3C28

Keeping only the lower 16 bits 

0x8ACF | 0x3C28

Finally I don't know how you are going to do the OR without writing the bitwise representation. I can help with the last hex. It will be F.

Upvotes: 2

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