Question

I am implementing a C function unsigned invert(unsigned x, int p, int n)
that is returning x with the n bits that begin at position p inverted, leaving the others unchanged.

#include <stdio.h>

unsigned invert(unsigned x, int p, int n);

int main()
{
    printf("%u\n", invert(11111111, 5, 4));
    printf("%u\n", invert(10, 2, 2));

    return 0;
}

unsigned invert(unsigned x, int p, int n)
{   
    return x^(~(~0<<n)<<p+1-n);
}

This is what I got so far and if I’m tracing the function through it should be right, but I keep getting 11111163 for the first test and 12 for the second test.

Answer 1

I think your program is working. Only thing you have to do is express the number in binary.

unsigned invert(unsigned x, int p, int n); 

int main()
{
    printf("%x\n", invert(0b11111111, 5, 4));
    printf("%x\n", invert(0b10, 2, 2));

return 0;

}

unsigned invert(unsigned x, int p, int n)

{   
     return x^(~(~0<<n)<<p+1-n);
}

Is this what you want?