bitwise-operation

bitwise-operation 教學與筆記。

題目 1

unsigned long v1 = 0x00001111;
unsigned long v2 = 0x00001202;
unsigned long v;
v = v1&(~v2);
v = v | v2;
ask: the value of v ?

• 過程 :

  v1  0001000100010001
  v2  0001001000000010
  
  v1  0001000100010001
  ~v2 1110110111111101
  
  v1&(~v2) 0000000100010001
  v2       0001001000000010
  v | v2   0001001100010011
              1   3   1   3
  
  Final v = 0x1313

• 實際驗證 :

  #include <stdio.h>
  
  void main(){
          unsigned long v1 = 0x00001111;
          unsigned long v2 = 0x00001202;
          unsigned long v;
          v = v1&(~v2);
          v = v | v2;
          printf("0x%lx\n", v); // 0x1313
  }

題目 2

• Setting a bit (Force nth bit to 1)

  #include <stdio.h>
  
  void main(){
      int a = 76;         // 1001100, DEC 76
      a |= (1UL << 4);
      printf("%d\n", a);  // 1011100, DEC 92
  }

• Clearing a bit (Force nth bit to 0)

  #include <stdio.h>
  
  void main(){
      int a = 76;         // 1001100, DEC 76
      a &= ~(1UL << 3);
      printf("%d\n", a);  // 1000100, DEC 68
  }

• Toggling a bit (Change nth bit “from 1 to 0” or “from 0 to 1”)

  #include <stdio.h>
  
  void main(){
      int a = 76;         // 1001100, DEC 76
      a ^= (1UL << 3);
      printf("%d\n", a);  // 1011100, DEC 92
  }

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