linux/include/asm-i386/checksum.h

#ifndef _I386_CHECKSUM_H
#define _I386_CHECKSUM_H

#include <linux/in6.h>

#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
 */
asmlinkage __wsum csum_partial(const void *buff, int len, __wsum sum);

/*
 * the same as csum_partial, but copies from src while it
 * checksums, and handles user-space pointer exceptions correctly, when needed.
 *
 * here even more important to align src and dst on a 32-bit (or even
 * better 64-bit) boundary
 */

asmlinkage __wsum csum_partial_copy_generic(const void *src, void *dst,
						  int len, __wsum sum, int *src_err_ptr, int *dst_err_ptr);

/*
 *	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__
__wsum csum_partial_copy_nocheck (const void *src, void *dst,
					int len, __wsum sum)
{
	return csum_partial_copy_generic ( src, dst, len, sum, NULL, NULL);
}

static __inline__
__wsum csum_partial_copy_from_user(const void __user *src, void *dst,
						int len, __wsum sum, int *err_ptr)
{
	might_sleep();
	return csum_partial_copy_generic((__force void *)src, dst,
					len, sum, err_ptr, NULL);
}

/*
 *	This is a version of ip_compute_csum() optimized for IP headers,
 *	which always checksum on 4 octet boundaries.
 *
 *	By Jorge Cwik <jorge@laser.satlink.net>, adapted for linux by
 *	Arnt Gulbrandsen.
 */
static inline __sum16 ip_fast_csum(const void *iph, unsigned int ihl)
{
	unsigned int sum;

	__asm__ __volatile__(
	    "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:				;\n"
	/* Since the input registers which are loaded with iph and ihl
	   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 (__force __sum16)sum;
}

/*
 *	Fold a partial checksum
 */

static inline __sum16 csum_fold(__wsum sum)
{
	__asm__(
		"addl %1, %0		;\n"
		"adcl $0xffff, %0	;\n"
		: "=r" (sum)
		: "r" ((__force u32)sum << 16),
		  "0" ((__force u32)sum & 0xffff0000)
	);
	return (__force __sum16)(~(__force u32)sum >> 16);
}

static inline __wsum csum_tcpudp_nofold(__be32 saddr, __be32 daddr,
					   unsigned short len,
					   unsigned short proto,
					   __wsum 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"((len + proto) << 8), "0"(sum));
    return sum;
}

/*
 * 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));
}

#define _HAVE_ARCH_IPV6_CSUM
static __inline__ __sum16 csum_ipv6_magic(const struct in6_addr *saddr,
					  const struct in6_addr *daddr,
					  __u32 len, unsigned short proto,
					  __wsum sum)
{
	__asm__(
		"addl 0(%1), %0		;\n"
		"adcl 4(%1), %0		;\n"
		"adcl 8(%1), %0		;\n"
		"adcl 12(%1), %0	;\n"
		"adcl 0(%2), %0		;\n"
		"adcl 4(%2), %0		;\n"
		"adcl 8(%2), %0		;\n"
		"adcl 12(%2), %0	;\n"
		"adcl %3, %0		;\n"
		"adcl %4, %0		;\n"
		"adcl $0, %0		;\n"
		: "=&r" (sum)
		: "r" (saddr), "r" (daddr),
		  "r"(htonl(len)), "r"(htonl(proto)), "0"(sum));

	return csum_fold(sum);
}

/*
 *	Copy and checksum to user
 */
#define HAVE_CSUM_COPY_USER
static __inline__ __wsum csum_and_copy_to_user(const void *src,
						     void __user *dst,
						     int len, __wsum sum,
						     int *err_ptr)
{
	might_sleep();
	if (access_ok(VERIFY_WRITE, dst, len))
		return csum_partial_copy_generic(src, (__force void *)dst, len, sum, NULL, err_ptr);

	if (len)
		*err_ptr = -EFAULT;

	return (__force __wsum)-1; /* invalid checksum */
}

#endif