base64 decoder

base64dec.cc

#include <iostream>
#include <bitset>
#include <vector>
#include <string>

int main(int argc, char *argv[])
{
  std::string table =
    "ABCDEFGHIJKLMNOPQRSTUVWXYZ"
    "abcdefghijklmnopqrstuvwxyz"
    "0123456789+/";
  std::string in,out;std::cin>>in;
  std::string::iterator iter=in.begin();
  std::bitset<24> data24;
  for(int i=0;i<in.size()/4;i++){
    data24|=(*iter=='=')?0:table.find(*iter,0);data24<<=6;++iter;
    data24|=(*iter=='=')?0:table.find(*iter,0);data24<<=6;++iter;
    data24|=(*iter=='=')?0:table.find(*iter,0);data24<<=6;++iter;
    data24|=(*iter=='=')?0:table.find(*iter,0);++iter;
    out.push_back((data24>>8*2).to_ulong());data24<<=8;
    out.push_back((data24>>8*2).to_ulong());data24<<=8;
    out.push_back((data24>>8*2).to_ulong());
  }
  std::cout<<out.c_str()<<std::endl;
  return 0;
}