[c][c++][note] Duff device

A Reusable Duff Device

#define DUFF_DEVICE_8(aCount, aAction) \
do { \
int count_ = (aCount); \
int times_ = (count_ + 7) >> 3; \
switch (count_ & 7){ \
case 0: do { aAction; \
case 7: aAction; \
case 6: aAction; \
case 5: aAction; \
case 4: aAction; \
case 3: aAction; \
case 2: aAction; \
case 1: aAction; \
} while (--times_ > 0); \
} \
} while (0)

Or just use template and lambda:

#include <iostream>                                                                       
                                                                                          
                                                                                          
template<typename INPUT>                                                                  
void duffDevice(INPUT process, int count)                                                 
{                                                                                         
   int n = (count + 7) >> 3;                                                              
   switch(count % 8)                                                                      
   {                                                                                      
      case 0: do { process();                                                             
      case 7: process();                                                                  
      case 6: process();                                                                  
      case 5: process();                                                                  
      case 4: process();                                                                  
      case 3: process();                                                                  
      case 2: process();                                                                  
      case 1: process();                                                                  
              } while(--n >0);                                                            
   };                                                                                     
}                                                                                         
                                                                                          
                                                                                          
int main()                                                                                
{                                                                                         
   duffDevice([]{std::cout << "poll data" << std::endl;}, 108);                           
}

Reference: Macro Note Clifford's Device GOTO statement Switch statement