checksum.h

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#ifndef __UM_CHECKSUM_H
#define __UM_CHECKSUM_H

#include <linux/string.h>
#include <linux/in6.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
 */
extern __wsum csum_partial(const void *buff, int len, __wsum 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__
__wsum csum_partial_copy_nocheck(const void *src, void *dst,
                       int len, __wsum sum)
{
    memcpy(dst, src, len);
    return csum_partial(dst, len, 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
 */

static __inline__
__wsum csum_partial_copy_from_user(const void __user *src, void *dst,
                     int len, __wsum sum, int *err_ptr)
{
    if (copy_from_user(dst, src, len)) {
        *err_ptr = -EFAULT;
        return (__force __wsum)-1;
    }

    return csum_partial(dst, len, sum);
}

static inline __sum16 csum_fold(__wsum sum)
{
    __asm__(
        "  addl %1,%0\n"
        "  adcl $0xffff,%0"
        : "=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));
}

static inline __sum16 ip_fast_csum(const void *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 (__force __sum16)sum;
}

#ifdef CONFIG_X86_32
# include "checksum_32.h"
#else
# include "checksum_64.h"
#endif

#endif