bit extraction

extract.c

#include <stdio.h>

#define bit_ext(val, m, n) 			\
	  int k = 1 << (m-1);			\
	  k = k | (k -1);			\
	  k = k ^ (1 << (n + 1));		\
	  int j = 1 << (n + 1);			\
	  j = j ^ (j - 1);			\
	  k = k ^ j;				\
	  val = val & k;			\
     	  val = val >> n;			\
int main()
{
     int i = 0xffff;
     bit_ext(i, 7, 4)
     printf("\n %d",i);
     return 0;
}