C_PRG_LANG_EX_2.7

#include <stdio.h>

// Inverts n bits starting with bit with number p
int invert(int x, int p, int n)
{
    unsigned int tmp = ~(0);

    tmp <<= n;
    for(int i = 0; i < p - n + 1; i++)
    {
        tmp <<= 1;
        tmp |= 1;
    }

    unsigned int zero = ~tmp; // 0000111100000
    tmp = ~(tmp) & x;
    x &= ~(zero);
    tmp |= (~zero);
    return (~tmp) | x;
}

int main(void)
{
    int p, n, x, y;
    x = 2679;
    y = 1473;
    p = 4;
    n = 5;

    printf("invert x = %i, p = %i, n = %i is %i\n", x, p, n, invert(x, p, n));
    printf("invert y = %i, p = %i, n = %i is %i\n", y, p, n, invert(y, p, n));


    return 0;
}