linux/arch/s390/include/asm/checksum.h

#ifndef _S390_CHECKSUM_H
#define _S390_CHECKSUM_H

/*
 *  include/asm-s390/checksum.h
 *    S390 fast network checksum routines
 *    see also arch/S390/lib/checksum.c
 *
 *  S390 version
 *    Copyright (C) 1999 IBM Deutschland Entwicklung GmbH, IBM Corporation
 *    Author(s): Ulrich Hild        (first version)
 *               Martin Schwidefsky (heavily optimized CKSM version)
 *               D.J. Barrow        (third attempt) 
 */

#include <asm/uaccess.h>

/*
 * 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
 */
static inline __wsum
csum_partial(const void *buff, int len, __wsum sum)
{
	register unsigned long reg2 asm("2") = (unsigned long) buff;
	register unsigned long reg3 asm("3") = (unsigned long) len;

	asm volatile(
		"0:	cksm	%0,%1\n"	/* do checksum on longs */
		"	jo	0b\n"
		: "+d" (sum), "+d" (reg2), "+d" (reg3) : : "cc", "memory");
	return sum;
}

/*
 * the same as csum_partial_copy, but copies from user space.
 *
 * here even more important to align src and dst on a 32-bit (or even
 * better 64-bit) boundary
 *
 * Copy from userspace and compute checksum.  If we catch an exception
 * then zero the rest of the buffer.
 */
static inline __wsum
csum_partial_copy_from_user(const void __user *src, void *dst,
                                          int len, __wsum sum,
                                          int *err_ptr)
{
	int missing;

	missing = copy_from_user(dst, src, len);
	if (missing) {
		memset(dst + len - missing, 0, missing);
		*err_ptr = -EFAULT;
	}
		
	return csum_partial(dst, len, sum);
}


static inline __wsum
csum_partial_copy_nocheck (const void *src, void *dst, int len, __wsum sum)
{
        memcpy(dst,src,len);
	return csum_partial(dst, len, sum);
}

/*
 *      Fold a partial checksum without adding pseudo headers
 */
static inline __sum16 csum_fold(__wsum sum)
{
	u32 csum = (__force u32) sum;

	csum += (csum >> 16) + (csum << 16);
	csum >>= 16;
	return (__force __sum16) ~csum;
}

/*
 *	This is a version of ip_compute_csum() optimized for IP headers,
 *	which always checksum on 4 octet boundaries.
 *
 */
static inline __sum16 ip_fast_csum(const void *iph, unsigned int ihl)
{
	return csum_fold(csum_partial(iph, ihl*4, 0));
}

/*
 * computes the checksum of the TCP/UDP pseudo-header
 * returns a 32-bit checksum
 */
static inline __wsum
csum_tcpudp_nofold(__be32 saddr, __be32 daddr,
                   unsigned short len, unsigned short proto,
                   __wsum sum)
{
	__u32 csum = (__force __u32)sum;

	csum += (__force __u32)saddr;
	if (csum < (__force __u32)saddr)
		csum++;

	csum += (__force __u32)daddr;
	if (csum < (__force __u32)daddr)
		csum++;

	csum += len + proto;
	if (csum < len + proto)
		csum++;

	return (__force __wsum)csum;
}

/*
 * computes the checksum of the TCP/UDP pseudo-header
 * returns a 16-bit checksum, already complemented
 */

static inline __sum16
csum_tcpudp_magic(__be32 saddr, __be32 daddr,
                  unsigned short len, unsigned short proto,
                  __wsum sum)
{
	return csum_fold(csum_tcpudp_nofold(saddr,daddr,len,proto,sum));
}

/*
 * this routine is used for miscellaneous IP-like checksums, mainly
 * in icmp.c
 */

static inline __sum16 ip_compute_csum(const void *buff, int len)
{
	return csum_fold(csum_partial(buff, len, 0));
}

#endif /* _S390_CHECKSUM_H */