Answer to Exercise 2-7, page 49 LINGUAGGIO C

Write a function invert(x,p,n) that returns x with the n bits that begin at position p inverted (i.e., 1 changed into 0 and vice versa), leaving the others unchanged.

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

/* main driver added, in a hurry while tired, by RJH. Better test driver suggestions are welcomed! */

#include <stdio.h>

int main(void)
{
  unsigned x;
  int p, n;

  for(x = 0; x < 700; x += 49)
    for(n = 1; n < 8; n++)
      for(p = 1; p < 8; p++)
        printf("%u, %d, %d: %u\n", x, n, p, invert(x, n, p));
  return 0;
}