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

unsigned long str2ip(char*s)
{ char*sp,*sp1,*sp2;
  int n1,n2,n3,n4;
  sp=strchr(s,'.');if(!sp)return 0;sp++;
  sp1=strchr(sp,'.');if(!sp1)return 0;sp1++;
  sp2=strchr(sp1,'.');if(!sp2)return 0;sp2++;
  n1=atoi(s);n2=atoi(sp);n3=atoi(sp1);n4=atoi(sp2);
  return (n1<<24)+(n2<<16)+(n3<<8)+n4;
}

unsigned long str2mask(int n)
{ unsigned long l=0;
  while(n>0){l>>=1;l|=0x80000000;n--;}
  return l;
}

char*ip2str(unsigned long ip)
{ static char sip[32];
  snprintf(sip,30,"%i.%i.%i.%i",
  (ip>>24)&0x000000FF,
  (ip>>16)&0x000000FF,
   (ip>>8)&0x000000FF,
      (ip)&0x000000FF);
  return sip;
}

void printmask2range(char*s)
{ char*sp;
  unsigned long ip;
  unsigned long mask,notmask;
  sp=strchr(s,'/');if(!sp){printf("Incorrect format.\n");return;}sp++;
  ip=str2ip(s);
  mask=str2mask(atoi(sp));
  notmask=mask^0xFFFFFFFF;
  printf("%s",ip2str(ip & mask));
  printf("-%s\n",ip2str(ip | notmask));
}

void printrange2mask(char*s1,char*s2)
{ char*sp;
  unsigned long ip1,ip2,ipmask;
  unsigned long mask=0;
  ip1=str2ip(s1);
  ip2=str2ip(s2);
  ipmask=0x80000000;
  for(mask=0;mask<33;mask++)
  {if( (ip1 & ipmask) != (ip2 & ipmask) )break;
   ipmask>>=1;
  }
  ipmask=str2mask(mask);
  printf("%s",ip2str(ip1 & ipmask));
  printf("/%i\n",mask);
}

void help()
{ printf(
"Usage: ipdiffmask IP/mask\n"
"       ipdiffmask IP IP\n"
"Converts between IP..IP and IP/bits network range representations.\n"
);
}

int main(int argc,char*argv[])
{
  if(argc<2){help();return 0;}
  if(argc>3){help();return 0;}
  if(!strcmp(argv[1],"-h")){help();return 0;}
  if(!strcmp(argv[1],"--help")){help();return 0;}
  if(argc==2){printmask2range(argv[1]);}
        else {printrange2mask(argv[1],argv[2]);}
  return 0;
}