Create a function to get n bits from position p - C Operator

C examples for Operator:Bit Operator

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Description

Create a function to get n bits from position p

Demo Code

#include <stdio.h>

unsigned getbits(unsigned x, int p, int n) {
   return (x >> (p + 1 - n)) & ~(~0 << n);
}

int bitcount(unsigned x) {
   int b = 0;//from ww w.j av  a2  s. com
   for (b = 0; x != 0; x >>= 1) {
      if (x & 01)
         b++;
   }
   return b;
}

int main() {
   int n;

   if (bitcount(072) != 4) /* 0111010 */
      printf("error 072\n");
   for (int i = 1; i <= 30; i++) {
      if (bitcount(3 << i) != 2)
         printf("error 3 << %d\n", i);
   }
   for (int i = 0; i < 25; i++) {
      n = 033 << i;   /* 011011 */
      if (getbits(n, i + 3, 3) != 5)
         printf("error getbits 1 %d\n", i);
      if (getbits(n, i + 1, 2) != 3)
         printf("error getbits 2 %d\n", i);
      if (getbits(n, i + 2, 1) != 0)
         printf("error getbits 3 %d\n", i);
   }
   return 0;
}

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