arch/um/include/sysdep-x86_64/checksum.h

/*
 * Licensed under the GPL
 */

#ifndef __UM_SYSDEP_CHECKSUM_H
#define __UM_SYSDEP_CHECKSUM_H

#include "linux/string.h"
#include "linux/in6.h"
#include "asm/uaccess.h"

extern unsigned csum_partial(const unsigned char *buff, unsigned len,
                             unsigned sum);

/*
 *	Note: when you get a NULL pointer exception here this means someone
 *	passed in an incorrect kernel address to one of these functions.
 *
 *	If you use these functions directly please don't forget the
 *	access_ok().
 */

static __inline__
unsigned int csum_partial_copy_nocheck(const unsigned char *src, unsigned char *dst,
				       int len, int sum)
{
	memcpy(dst, src, len);
	return(csum_partial(dst, len, sum));
}

static __inline__
unsigned int csum_partial_copy_from_user(const unsigned char *src,
                                         unsigned char *dst, int len, int sum,
                                         int *err_ptr)
{
        if(copy_from_user(dst, src, len)){
                *err_ptr = -EFAULT;
                return(-1);
        }
        return csum_partial(dst, len, sum);
}

/**
 * csum_fold - Fold and invert a 32bit checksum.
 * sum: 32bit unfolded sum
 *
 * Fold a 32bit running checksum to 16bit and invert it. This is usually
 * the last step before putting a checksum into a packet.
 * Make sure not to mix with 64bit checksums.
 */
static inline unsigned int csum_fold(unsigned int sum)
{
	__asm__(
		"  addl %1,%0\n"
		"  adcl $0xffff,%0"
		: "=r" (sum)
		: "r" (sum << 16), "0" (sum & 0xffff0000)
	);
	return (~sum) >> 16;
}

/**
 * csum_tcpup_nofold - Compute an IPv4 pseudo header checksum.
 * @saddr: source address
 * @daddr: destination address
 * @len: length of packet
 * @proto: ip protocol of packet
 * @sum: initial sum to be added in (32bit unfolded)
 *
 * Returns the pseudo header checksum the input data. Result is
 * 32bit unfolded.
 */
static inline unsigned long
csum_tcpudp_nofold(unsigned saddr, unsigned daddr, unsigned short len,
		   unsigned short proto, unsigned int sum)
{
	asm("  addl %1, %0\n"
	    "  adcl %2, %0\n"
	    "  adcl %3, %0\n"
	    "  adcl $0, %0\n"
		: "=r" (sum)
	    : "g" (daddr), "g" (saddr), "g" ((ntohs(len)<<16)+proto*256), "0" (sum));
    return sum;
}

/*
 * computes the checksum of the TCP/UDP pseudo-header
 * returns a 16-bit checksum, already complemented
 */
static inline unsigned short int csum_tcpudp_magic(unsigned long saddr,
						   unsigned long daddr,
						   unsigned short len,
						   unsigned short proto,
						   unsigned int sum)
{
	return csum_fold(csum_tcpudp_nofold(saddr,daddr,len,proto,sum));
}

/**
 * ip_fast_csum - Compute the IPv4 header checksum efficiently.
 * iph: ipv4 header
 * ihl: length of header / 4
 */
static inline unsigned short ip_fast_csum(unsigned char *iph, unsigned int ihl)
{
	unsigned int sum;

	asm(	"  movl (%1), %0\n"
		"  subl $4, %2\n"
		"  jbe 2f\n"
		"  addl 4(%1), %0\n"
		"  adcl 8(%1), %0\n"
		"  adcl 12(%1), %0\n"
		"1: adcl 16(%1), %0\n"
		"  lea 4(%1), %1\n"
		"  decl %2\n"
		"  jne	1b\n"
		"  adcl $0, %0\n"
		"  movl %0, %2\n"
		"  shrl $16, %0\n"
		"  addw %w2, %w0\n"
		"  adcl $0, %0\n"
		"  notl %0\n"
		"2:"
	/* Since the input registers which are loaded with iph and ipl
	   are modified, we must also specify them as outputs, or gcc
	   will assume they contain their original values. */
	: "=r" (sum), "=r" (iph), "=r" (ihl)
	: "1" (iph), "2" (ihl)
	: "memory");
	return(sum);
}

static inline unsigned add32_with_carry(unsigned a, unsigned b)
{
        asm("addl %2,%0\n\t"
            "adcl $0,%0"
            : "=r" (a)
            : "0" (a), "r" (b));
        return a;
}

extern unsigned short ip_compute_csum(unsigned char * buff, int len);

#endif