text: #include <arpa/inet.h>
  #ifdef __cplusplus
  extern "C" {
  #endif
  
  /*
   * Copyright (C) 1996-2001  Internet Software Consortium.
   *
   * Permission to use, copy, modify, and distribute this software for any
   * purpose with or without fee is hereby granted, provided that the above
   * copyright notice and this permission notice appear in all copies.
   *
   * THE SOFTWARE IS PROVIDED "AS IS" AND INTERNET SOFTWARE CONSORTIUM
   * DISCLAIMS ALL WARRANTIES WITH REGARD TO THIS SOFTWARE INCLUDING ALL
   * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS. IN NO EVENT SHALL
   * INTERNET SOFTWARE CONSORTIUM BE LIABLE FOR ANY SPECIAL, DIRECT,
   * INDIRECT, OR CONSEQUENTIAL DAMAGES OR ANY DAMAGES WHATSOEVER RESULTING
   * FROM LOSS OF USE, DATA OR PROFITS, WHETHER IN AN ACTION OF CONTRACT,
   * NEGLIGENCE OR OTHER TORTIOUS ACTION, ARISING OUT OF OR IN CONNECTION
   * WITH THE USE OR PERFORMANCE OF THIS SOFTWARE.
  */
  
  #ifndef HAVE_INET_NTOP
  #define NS_INT16SZ       2
  #define NS_INADDRSZ     4
  #define NS_IN6ADDRSZ    16
  
  /*
   * WARNING: Don't even consider trying to compile this on a system where
   * sizeof(int) < 4.  sizeof(int) > 4 is fine; all the world's not a VAX.
   */
  
  
  /* char *
   * isc_net_ntop(af, src, dst, size)
   *      convert a network format address to presentation format.
   * return:
   *      pointer to presentation format address (`dst'), or NULL (see errno).
   * author:
   *      Paul Vixie, 1996.
   */
  const char* 
  inet_ntop(int af, const void *src, char *dst, socklen_t size) {
      switch ( af ) {
          case AF_INET:
              return(inet_ntop4(src, dst, size));
  #ifdef HAVE_IPV6
          case AF_INET6:
              return(inet_ntop6(src, dst, size));
  #endif
          default:
              return NULL;
      }
      /* NOTREACHED */
  }
  
  /* const char *
   * inet_ntop4(src, dst, size)
   *      format an IPv4 address
   * return:
   *      `dst' (as a const)
   * notes:
   *      (1) uses no statics
   *      (2) takes a unsigned char* not an in_addr as input
   * author:
   *      Paul Vixie, 1996.
   */
  const char*
  inet_ntop4(const unsigned char *src, char *dst, socklen_t size) {
      static const char *fmt = "%u.%u.%u.%u";
      char tmp[sizeof "255.255.255.255"];
  
      if ( (size_t)sprintf(tmp, fmt, src[0], src[1], src[2], src[3]) >= size ) {
          return NULL;
      }
      strcpy(dst, tmp);
  
      return dst;
  }
  
  /* const char *
   * isc_inet_ntop6(src, dst, size)
   *      convert IPv6 binary address into presentation (printable) format
   * author:
   *      Paul Vixie, 1996.
   */
  #ifdef HAVE_IPV6
  const char*
  inet_ntop6(const unsigned char *src, char *dst, socklen_t size) {
      /*
       * Note that int32_t and int16_t need only be "at least" large enough
       * to contain a value of the specified size.  On some systems, like
       * Crays, there is no such thing as an integer variable with 16 bits.
       * Keep this in mind if you think this function should have been coded
       * to use pointer overlays.  All the world's not a VAX.
       */
      char tmp[sizeof "ffff:ffff:ffff:ffff:ffff:ffff:255.255.255.255"], *tp;
      struct {
          int base, len;
      } best, cur;
      unsigned int words[NS_IN6ADDRSZ / NS_INT16SZ];
      int i;
  
      /*
       * Preprocess:
       *      Copy the input (bytewise) array into a wordwise array.
       *      Find the longest run of 0x00's in src[] for :: shorthanding.
       */
      memset(words, '\0', sizeof words);
      for ( i = 0; i < NS_IN6ADDRSZ; i++ )
          words[i / 2] |= (src[i] << ((1 - (i % 2)) << 3));
      best.base = -1;
      cur.base = -1;
      for ( i = 0; i < (NS_IN6ADDRSZ / NS_INT16SZ); i++ ) {
          if ( words[i] == 0 ) {
              if ( cur.base == -1 )
                  cur.base = i, cur.len = 1;
              else
                  cur.len++;
          } else {
              if ( cur.base != -1 ) {
                  if ( best.base == -1 || cur.len > best.len )
                      best = cur;
                  cur.base = -1;
              }
          }
      }
      if ( cur.base != -1 ) {
          if ( best.base == -1 || cur.len > best.len )
              best = cur;
      }
      if ( best.base != -1 && best.len < 2 )
          best.base = -1;
  
      /*
       * Format the result.
       */
      tp = tmp;
      for ( i = 0; i < (NS_IN6ADDRSZ / NS_INT16SZ); i++ ) {
          /* Are we inside the best run of 0x00's? */
          if ( best.base != -1 && i >= best.base &&
               i < (best.base + best.len) ) {
              if ( i == best.base )
                  *tp++ = ':';
              continue;
          }
          /* Are we following an initial run of 0x00s or any real hex? */
          if ( i != 0 )
              *tp++ = ':';
          /* Is this address an encapsulated IPv4? */
          if ( i == 6 && best.base == 0 &&
               (best.len == 6 || (best.len == 5 && words[5] == 0xffff)) ) {
              if ( !inet_ntop4(src+12, tp,
                               sizeof tmp - (tp - tmp)) )
                  return NULL;
              tp += strlen(tp);
              break;
          }
          tp += sprintf(tp, "%x", words[i]);
      }
      /* Was it a trailing run of 0x00's? */
      if ( best.base != -1 && (best.base + best.len) ==
           (NS_IN6ADDRSZ / NS_INT16SZ) )
          *tp++ = ':';
      *tp++ = '\0';
  
      /*
       * Check for overflow, copy, and we're done.
       */
      if ( (size_t)(tp - tmp) > size ) {
          errno = ENOSPC;
          return NULL;
      }
      strcpy(dst, tmp);
      return dst;
  }
  #endif /* HAVE_IPV6 */
  #endif /* HAVE_INET_NTOP */
  
  #ifdef __cplusplus
  } /* end extern "C" */
  #endif
  
  