checksum.c

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/*
 * Network checksum routines
 *
 * Copyright (C) 1999 Hewlett-Packard Co
 * Copyright (C) 1999 Stephane Eranian <[e-mail]>
 *
 * Most of the code coming from arch/alpha/lib/checksum.c
 *
 * This file contains network checksum routines that are better done
 * in an architecture-specific manner due to speed..
 */
 
#include <linux/string.h>

#include <asm/byteorder.h>

static inline unsigned short
from64to16(unsigned long x)
{
	/* add up 32-bit words for 33 bits */
	x = (x & 0xffffffff) + (x >> 32);
	/* add up 16-bit and 17-bit words for 17+c bits */
	x = (x & 0xffff) + (x >> 16);
	/* add up 16-bit and 2-bit for 16+c bit */
	x = (x & 0xffff) + (x >> 16);
	/* add up carry.. */
	x = (x & 0xffff) + (x >> 16);
	return x;
}

/*
 * computes the checksum of the TCP/UDP pseudo-header
 * returns a 16-bit checksum, already complemented.
 */
unsigned short int csum_tcpudp_magic(unsigned long saddr,
				   unsigned long daddr,
				   unsigned short len,
				   unsigned short proto,
				   unsigned int sum)
{
	return ~from64to16(saddr + daddr + sum +
		((unsigned long) ntohs(len) << 16) +
		((unsigned long) proto << 8));
}

unsigned int csum_tcpudp_nofold(unsigned long saddr,
				   unsigned long daddr,
				   unsigned short len,
				   unsigned short proto,
				   unsigned int sum)
{
	unsigned long result;

	result = (saddr + daddr + sum +
		  ((unsigned long) ntohs(len) << 16) +
		  ((unsigned long) proto << 8));

	/* Fold down to 32-bits so we don't loose in the typedef-less 
	   network stack.  */
	/* 64 to 33 */
	result = (result & 0xffffffff) + (result >> 32);
	/* 33 to 32 */
	result = (result & 0xffffffff) + (result >> 32);
	return result;
}

extern unsigned long do_csum(const unsigned char *, unsigned int, unsigned int);
extern unsigned long do_csum_c(const unsigned char *, unsigned int, unsigned int);

/*
 *	This is a version of ip_compute_csum() optimized for IP headers,
 *	which always checksum on 4 octet boundaries.
 */
unsigned short ip_fast_csum(unsigned char * iph, unsigned int ihl)
{
	return ~do_csum(iph,ihl*4,0);
}

/*
 * computes the checksum of a memory block at buff, length len,
 * and adds in "sum" (32-bit)
 *
 * returns a 32-bit number suitable for feeding into itself
 * or csum_tcpudp_magic
 *
 * this function must be called with even lengths, except
 * for the last fragment, which may be odd
 *
 * it's best to have buff aligned on a 32-bit boundary
 */
unsigned int csum_partial(const unsigned char * buff, int len, unsigned int sum)
{
	unsigned long result = do_csum(buff, len, 0);

	/* add in old sum, and carry.. */
	result += sum;
	/* 32+c bits -> 32 bits */
	result = (result & 0xffffffff) + (result >> 32);
	return result;
}


/*
 * this routine is used for miscellaneous IP-like checksums, mainly
 * in icmp.c
 */
unsigned short ip_compute_csum(unsigned char * buff, int len)
{
	return ~do_csum(buff,len, 0);
}