ospf_old_ip_dependencies.c

来自「vxworks下ospf协议栈」· C语言 代码 · 共 118 行

/* ospf_old_ip_dependencies.c */

/* Copyright 2000 Wind River Systems, Inc. */

/*modification history
___________________
 */

/* 
DESCRIPTION
ospf_old_ip_dependencies.c is used for checksums for IP.
This file is used whenever the IP checksum needs to be evaluated.
*/

#include "ospf.h"

/*************************************************************************/
static USHORT end_around_carry (ULONG sum);				/* Carries in high order 16 bits */
static USHORT calculate_word_checksum (USHORT *usptr_short, USHORT length);
/****************************************************************************/
static USHORT end_around_carry (ULONG sum)				/* Carries in high order 16 bits */
{
	USHORT csum;
	USHORT return_value;

	OSPF_PRINTF_DEBUG (OSPF_DEBUG_PRINTF, "OSPF: Entering end_around_carry\r\n");

	csum = (USHORT) (sum >> 16);

	while (csum != 0x0000)
		{
		sum = csum + (sum & 0xffffL);

		csum = (USHORT) (sum >> 16);
		}

	/* Chops to 16 bits */

	return_value = (USHORT) (sum & 0x0000ffffL);

	return (return_value);
}
/****************************************************************************/
static USHORT calculate_word_checksum (USHORT *usptr_short, USHORT length)
{
	ULONG sum;
	USHORT result;

	OSPF_PRINTF_DEBUG (OSPF_DEBUG_PRINTF, "OSPF: Entering calculate_word_checksum\r\n");

	sum = 0x00000000L;

	while (length != 0x0000)
		{
		--length;

		sum += *usptr_short;

		++usptr_short;
		}

	result = end_around_carry (sum);

	return (result);
}

/*************************************************************************/
/* the data order is assumed to be network order. */
USHORT calculate_ip_checksum (PSEUDO_IP_PARAMETERS *sptr_pseudo_header, BYTE *bptr_start_from, USHORT length)
{
	USHORT word_checksum;
	ULONG sum;
	ULONG checksum;
	USHORT return_value;

	OSPF_PRINTF_DEBUG (OSPF_DEBUG_PRINTF, "OSPF: Entering calculate_ip_checksum\r\n");

	sum = 0x00000000L;

	if (sptr_pseudo_header != NULL)
		{	
		word_checksum = calculate_word_checksum ((USHORT *) sptr_pseudo_header, (USHORT) (sizeof (PSEUDO_IP_PARAMETERS)) >> 1);

		sum = word_checksum;
		}

	checksum = 0x00000000L;

	if (length > 1)
		{
		/* ptr_start_from must be on short word boundary */

		word_checksum = calculate_word_checksum ((USHORT *) bptr_start_from, (USHORT) (length >> 1));

		checksum += word_checksum;
		}

	/* Handle odd trailing byte */

	if ((length & 0x0001) != 0x0000)
		{
#if (_BYTE_ORDER == _LITTLE_ENDIAN )
		checksum += (unsigned char) (bptr_start_from[--length]);
#else
		checksum += (USHORT)(((unsigned char) (bptr_start_from[--length])) << 8);
#endif
		}

	sum += checksum;

	/* Do final end-around carry, complement and return */

	return_value = (USHORT) (~end_around_carry (sum) & 0xffff);

	return (return_value);
}
/*************************************************************************/