dist/ipf/lib/count4bits.c

   1 /*      $NetBSD$        */
   2
   3 /*
   4  * Copyright (C) 2002 by Darren Reed.
   5  *
   6  * See the IPFILTER.LICENCE file for details on licencing.
   7  *
   8  * Id: count4bits.c,v 1.1.4.1 2006/06/16 17:20:57 darrenr Exp
   9  */
  10
  11 #include "ipf.h"
  12
  13
  14 /*
  15  * count consecutive 1's in bit mask.  If the mask generated by counting
  16  * consecutive 1's is different to that passed, return -1, else return #
  17  * of bits.
  18  */
  19 int     count4bits(ip)
  20 u_int   ip;
  21 {
  22         int cnt = 0, i, j;
  23         u_int ipn;
  24
  25         ip = ipn = ntohl(ip);
  26         for (i = 32; i; i--, ipn *= 2)
  27                 if (ipn & 0x80000000)
  28                         cnt++;
  29                 else
  30                         break;
  31         ipn = 0;
  32         for (i = 32, j = cnt; i; i--, j--) {
  33                 ipn *= 2;
  34                 if (j > 0)
  35                         ipn++;
  36         }
  37         if (ipn == ip)
  38                 return cnt;
  39         return -1;
  40 }