usr/src/cmd/ipf/lib/common/count4bits.c

   1 /*
   2  * Copyright (C) 1993-2001 by Darren Reed.
   3  *
   4  * See the IPFILTER.LICENCE file for details on licencing.
   5  *
   6  * $Id: count4bits.c,v 1.1 2002/06/15 04:46:39 darrenr Exp $
   7  */
   8
   9 #include "ipf.h"
  10
  11
  12 /*
  13  * count consecutive 1's in bit mask.  If the mask generated by counting
  14  * consecutive 1's is different to that passed, return -1, else return #
  15  * of bits.
  16  */
  17 int     count4bits(ip)
  18 u_int   ip;
  19 {
  20         int cnt = 0, i, j;
  21         u_int ipn;
  22
  23         ip = ipn = ntohl(ip);
  24         for (i = 32; i; i--, ipn *= 2)
  25                 if (ipn & 0x80000000)
  26                         cnt++;
  27                 else
  28                         break;
  29         ipn = 0;
  30         for (i = 32, j = cnt; i; i--, j--) {
  31                 ipn *= 2;
  32                 if (j > 0)
  33                         ipn++;
  34         }
  35         if (ipn == ip)
  36                 return cnt;
  37         return -1;
  38 }