external/ibm-public/postfix/dist/src/util/mask_addr.c

   1 /*      $NetBSD$        */
   2
   3 /*++
   4 /* NAME
   5 /*      mask_addr 3
   6 /* SUMMARY
   7 /*      address bit banging
   8 /* SYNOPSIS
   9 /*      #include <mask_addr.h>
  10 /*
  11 /*      void    mask_addr(addr_bytes, addr_byte_count, network_bits)
  12 /*      unsigned char *addr_bytes;
  13 /*      unsigned addr_byte_count;
  14 /*      unsigned network_bits;
  15 /* DESCRIPTION
  16 /*      mask_addr() clears all the host bits in the specified
  17 /*      address.  The code can handle addresses of any length,
  18 /*      and bytes of any width.
  19 /*
  20 /*      Arguments:
  21 /* .IP addr_bytes
  22 /*      The network address in network byte order.
  23 /* .IP addr_byte_count
  24 /*      The network address length in bytes.
  25 /* .IP network_bits
  26 /*      The number of initial bits that will not be cleared.
  27 /* DIAGNOSTICS
  28 /*      Fatal errors: the number of network bits exceeds the address size.
  29 /* LICENSE
  30 /* .ad
  31 /* .fi
  32 /*      The Secure Mailer license must be distributed with this software.
  33 /* AUTHOR(S)
  34 /*      Wietse Venema
  35 /*      IBM T.J. Watson Research
  36 /*      P.O. Box 704
  37 /*      Yorktown Heights, NY 10598, USA
  38 /*--*/
  39
  40 /* System library. */
  41
  42 #include <sys_defs.h>
  43 #include <limits.h>                     /* CHAR_BIT */
  44
  45 /* Utility library. */
  46
  47 #include <msg.h>
  48 #include <mask_addr.h>
  49
  50 /* mask_addr - mask off a variable-length address */
  51
  52 void    mask_addr(unsigned char *addr_bytes,
  53                           unsigned addr_byte_count,
  54                           unsigned network_bits)
  55 {
  56     unsigned char *p;
  57
  58     if (network_bits > addr_byte_count * CHAR_BIT)
  59         msg_panic("mask_addr: address byte count %d too small for bit count %d",
  60                   addr_byte_count, network_bits);
  61
  62     p = addr_bytes + network_bits / CHAR_BIT;
  63     network_bits %= CHAR_BIT;
  64
  65     if (network_bits != 0)
  66         *p++ &= ~0 << (CHAR_BIT - network_bits);
  67
  68     while (p < addr_bytes + addr_byte_count)
  69         *p++ = 0;
  70 }