知識+ 大陣列中bit處理(可跨byte)

//===================================================================
// 20090331 知識 +
// http://tw.knowledge.yahoo.com/question/question?qid=1509033101375
// 發問者 : http://tw.knowledge.yahoo.com/my/my?show=AE03178958
//=================================================================== 

#include <stdio.h>
#include <stdlib.h>

#pragma pack(1)
struct BYTE
{
   unsigned char Byte;
   unsigned int getBits(unsigned int i, unsigned char l=1 )
   { 
      unsigned int rtn = 0;
      if (l>32l==0) return 0;
      int n=i/8;
      int b=i%8;
      unsigned char * p = (unsigned char *)((&Byte)+n);
      while(l-->0)
      {
         rtn = ((unsigned int)(((*p)>>(7-b))&1))<<l;
         if (++b==8){ b=0; p++;}
      }
      return rtn;
   }
   void setBits(unsigned int i,unsigned int d, unsigned char l=1)
   {
      if (l>32l==0) return;
      int n=i/8;
      int b=i%8;
      unsigned char * p = (unsigned char *)((&Byte)+n);
      while(l-->0)
      {
         if ((d>>l)&1) *p = 0x80>>b;
         else *p &= ~(0x80>>b);
         if (++b==8){ b=0; p++;}
      }
   }
};

int main()
{
  BYTE a[32];

  printf( "\n a[] size = %d, BYTE size= %d\n", sizeof(a), sizeof(BYTE));
  for(int i=0; i<30; i++)
     a[i].Byte=0;
 
  for(int i=0; i<240; i++)
    a[0].setBits(i,(i%3==0)?1:0);

  printf ("\nDump Buffer:\n");
  for(int i=0; i<30; i++)
   printf("0x%02X%c",a[i].Byte, (i%10==9)? '\n': ' ');

  // 
  printf ("\nSet & Get:");
  for(int i=0; i<240; i+=3)
  {
     a[0].setBits(i, (i/3%8), 3);
     printf("%cx%01X", (i%60==0)? '\n': ' ', a[0].getBits(i,3) );
  }

  printf ("\n\nDump Buffer:\n");
  for(int i=0; i<30; i++)
   printf("0x%02X%c",a[i].Byte, (i%10==9)? '\n': ' ');
  return 0;
}

//=============================================================================