#include <stdio.h>

unsigned int setbits(unsigned int x, int p, int n, unsigned int y)
{
  unsigned int y_n = y & ~(~0 << n);
  unsigned int mask = ~(~(~0 << n) << p);
  unsigned int x_ret = x & mask;
  x_ret = x_ret | (y_n << p);

  return x_ret;
}

int main(void)
{
  /*
   * x = 0x33 = 110011
   *             ^^^
   *             nnn
   * y = 0x4e = 1001110
   *                ^^^
   *                nnn
   *
   * result = 0x3b = 111011
   */
  printf("%x\n", setbits(0x33, 2, 3, 0x4e));
}