arch/arc/lib/checksum.c

/*
 * Copyright (C) 2004, 2007-2010, 2011-2012 Synopsys, Inc. (www.synopsys.com)
 *
 * This program is free software; you can redistribute it and/or modify
 * it under the terms of the GNU General Public License version 2 as
 * published by the Free Software Foundation.
 *
 * For ARC: Amit Shah <amitshah@gmx.net>
 * People who wrote arch/m68knommu/lib/checksum.c
 */

#include <linux/module.h>
#include <net/checksum.h>
#include <asm/checksum.h>

static inline unsigned short from32to16(unsigned long x)
{
	/* add up 16-bit and 16-bit for 16+c bit */
	x = (x & 0xffff) + (x >> 16);
	/* add up carry.. */
	x = (x & 0xffff) + (x >> 16);
	return x;
}

static unsigned long do_csum(const unsigned char *buff, int len)
{
	int odd, count;
	unsigned long result = 0;

	if (len <= 0)
		goto out;
	odd = 1 & (unsigned long)buff;
	if (odd) {
		result = be16_to_cpu(*buff);
		len--;
		buff++;
	}
	count = len >> 1;	/* nr of 16-bit words.. */
	if (count) {
		if (2 & (unsigned long)buff) {
			result += *(unsigned short *)buff;
			count--;
			len -= 2;
			buff += 2;
		}
		count >>= 1;	/* nr of 32-bit words.. */
		if (count) {
			unsigned long carry = 0;
			do {
				unsigned long w = *(unsigned long *)buff;
				count--;
				buff += 4;
				result += carry;
				result += w;
				carry = (w > result);
			} while (count);
			result += carry;
			result = (result & 0xffff) + (result >> 16);
		}
		if (len & 2) {
			result += *(unsigned short *)buff;
			buff += 2;
		}
	}
	if (len & 1)
		result += le16_to_cpu(*buff);
	result = from32to16(result);
	if (odd)
		result = ((result >> 8) & 0xff) | ((result & 0xff) << 8);
      out:
	return result;
}

/*
 * 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 void *buff, int len, unsigned int sum)
{
	unsigned int result = do_csum(buff, len);

	/* add in old sum, and carry.. */
	result += sum;
	if (sum > result)
		result += 1;
	return result;
}
EXPORT_SYMBOL(csum_partial);

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

/*
 * copy from ds while checksumming, otherwise like csum_partial
 */
unsigned int csum_partial_copy(const char *src, char *dst, int len, int sum)
{
	memcpy(dst, src, len);
	return csum_partial(dst, len, sum);
}

/*
 * copy from fs while checksumming, otherwise like csum_partial
 */
unsigned int
csum_partial_copy_from_user(const char *src, char *dst, int len, int sum,
			    int *csum_err)
{
	int missing;

	missing = copy_from_user(dst, src, len);

	if (missing) {
		memset(dst + len - missing, 0, missing);
		*csum_err = -EFAULT;
	}

	return csum_partial(dst, len, sum);

}