pimd/pim_util.c

/*
  PIM for Quagga
  Copyright (C) 2008  Everton da Silva Marques

  This program is free software; you can redistribute it and/or modify
  it under the terms of the GNU General Public License as published by
  the Free Software Foundation; either version 2 of the License, or
  (at your option) any later version.

  This program is distributed in the hope that it will be useful, but
  WITHOUT ANY WARRANTY; without even the implied warranty of
  MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
  General Public License for more details.
  
  You should have received a copy of the GNU General Public License
  along with this program; see the file COPYING; if not, write to the
  Free Software Foundation, Inc., 51 Franklin St, Fifth Floor, Boston,
  MA 02110-1301 USA
  
  $QuaggaId: $Format:%an, %ai, %h$ $
*/

#include "pim_util.h"

/*
  RFC 3376: 4.1.7. QQIC (Querier's Query Interval Code)
  
  If QQIC < 128,  QQI = QQIC
  If QQIC >= 128, QQI = (mant | 0x10) << (exp + 3)
  
  0 1 2 3 4 5 6 7
  +-+-+-+-+-+-+-+-+
  |1| exp | mant  |
  +-+-+-+-+-+-+-+-+
  
  Since exp=0..7 then (exp+3)=3..10, then QQI has
  one of the following bit patterns:
  
  exp=0: QQI = 0000.0000.1MMM.M000
  exp=1: QQI = 0000.0001.MMMM.0000
  ...
  exp=6: QQI = 001M.MMM0.0000.0000
  exp=7: QQI = 01MM.MM00.0000.0000
  --------- ---------
  0x4  0x0  0x0  0x0
*/
uint8_t igmp_msg_encode16to8(uint16_t value)
{
  uint8_t code;

  if (value < 128) {
    code = value;
  }
  else {
    uint16_t mask = 0x4000;
    uint8_t  exp;
    uint16_t mant;
    for (exp = 7; exp > 0; --exp) {
      if (mask & value)
	break;
      mask >>= 1;
    }
    mant = 0x000F & (value >> (exp + 3));
    code = ((uint8_t) 1 << 7) | ((uint8_t) exp << 4) | (uint8_t) mant;
  }

  return code;
}

/*
  RFC 3376: 4.1.7. QQIC (Querier's Query Interval Code)
  
  If QQIC < 128,  QQI = QQIC
  If QQIC >= 128, QQI = (mant | 0x10) << (exp + 3)
  
  0 1 2 3 4 5 6 7
  +-+-+-+-+-+-+-+-+
  |1| exp | mant  |
  +-+-+-+-+-+-+-+-+
*/
uint16_t igmp_msg_decode8to16(uint8_t code)
{
  uint16_t value;

  if (code < 128) {
    value = code;
  }
  else {
    uint16_t mant = (code & 0x0F);
    uint8_t  exp  = (code & 0x70) >> 4;
    value = (mant | 0x10) << (exp + 3);
  }

  return value;
}

#ifndef PIM_USE_QUAGGA_INET_CHECKSUM
/*
  RFC 3376: 4.1.2. Checksum

  The Checksum is the 16-bit one's complement of the one's complement
  sum of the whole IGMP message (the entire IP payload).  For
  computing the checksum, the Checksum field is set to zero.  When
  receiving packets, the checksum MUST be verified before processing a
  packet.  [RFC-1071]
*/
uint16_t pim_inet_checksum(const char *buf, int size)
{
  const uint16_t *ptr;
  uint32_t        sum;
  uint16_t        checksum;

  ptr = (const uint16_t *) buf;
  sum = 0;
  while (size > 1) {
    sum += *ptr;
    ++ptr;
    size -= 2;
  }

  /* Add left-over byte, if any */
  if (size > 0)
    sum += (uint16_t) *(const uint8_t *) ptr;

  /* Fold 32-bit sum to 16 bits */
  sum = (sum & 0xffff) + (sum >> 16);

  checksum = ~sum;

  return checksum;
}
#endif /* PIM_USE_QUAGGA_INET_CHECKSUM */