index_convert_v2.cpp

#include <iostream>

/*
 * 原symbol_code最大允许7个大写字符，可以用5个位表示一个大写字符，5*7=35，也就是用5个字节就可以容纳了。
 * 天数为1-365，用2个字节。
 */

uint64_t symbol_code;
uint64_t day;


uint64_t index_encode( uint64_t sym, uint64_t day){
   uint64_t res = 0;
   for ( int i = 0; sym & 0xFF && i < 7; i++ ) {
      res |= (sym & 0x1F) << (5 * i);
      sym >>= 8;
   }

   res <<= 16;
   res |= day & 0xFFFF;
   return res;
}


std::tuple<uint64_t ,uint64_t > index_decode(uint64_t index){

   uint64_t symbol = 0, day = 0;
   day = index & 0xFFFF;
   index >>= 16;
   symbol = 0;

   for ( int i = 0; index & 0x1F && i < 7; i++ ) {
      symbol |= (index & 0x1F) << (8 * i);
      index >>= 5;
   }

   return { symbol, day };
}


int main() {

   symbol_code = 0x0101010101;
   uint64_t index = index_encode( symbol_code, 255 );

   uint64_t sym1 = 0;
   uint64_t day1 = 0;
   std::tie( sym1, day1) = index_decode(index);


   if (sym1 == symbol_code && day1 == 255)
      std::cout << "Good" << std::endl;
   else
      std::cout << "Bad!" << std::endl;

   return 0;
}