#include <string>
using std::string;

inline string to_hex(unsigned char v){
  char buf[3]={0,0,0};
  sprintf(buf,"%02x",v);
  return buf;
}

inline char from_hex(char c1,char c2){
  char buf[3]={c1,c2,0};
  size_t v;
  sscanf(buf,"%02x",&v);
  return (char&)v;
}

inline string str2hex(const string&s)
{
  string out;
  out.reserve(s.size()*2);
  for(size_t i=0;i<s.size();i++)out+=to_hex((unsigned char&)s[i]);
  return out;
}

inline string hex2str(const string&s){
  string out;
  out.reserve(s.size()/2);
  for(size_t i=0;i<s.size();i+=2){
    out.push_back(from_hex(s[i],s[i+1]));
  }
  return out;
}