checksum.c

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/*
 * arch/alpha/lib/checksum.c
 *
 * This file contains network checksum routines that are better done
 * in an architecture-specific manner due to speed..
 * Comments in other versions indicate that the algorithms are from RFC1071
 *
 * accelerated versions (and 21264 assembly versions ) contributed by
 *  Rick Gorton <[email protected]>
 */
 
#include <linux/module.h>
#include <linux/string.h>

#include <asm/byteorder.h>

static inline unsigned short from64to16(unsigned long x)
{
    /* Using extract instructions is a bit more efficient
       than the original shift/bitmask version.  */

    union {
        unsigned long   ul;
        unsigned int    ui[2];
        unsigned short  us[4];
    } in_v, tmp_v, out_v;

    in_v.ul = x;
    tmp_v.ul = (unsigned long) in_v.ui[0] + (unsigned long) in_v.ui[1];

    /* Since the bits of tmp_v.sh[3] are going to always be zero,
       we don't have to bother to add that in.  */
    out_v.ul = (unsigned long) tmp_v.us[0] + (unsigned long) tmp_v.us[1]
            + (unsigned long) tmp_v.us[2];

    /* Similarly, out_v.us[2] is always zero for the final add.  */
    return out_v.us[0] + out_v.us[1];
}

/*
 * computes the checksum of the TCP/UDP pseudo-header
 * returns a 16-bit checksum, already complemented.
 */
__sum16 csum_tcpudp_magic(__be32 saddr, __be32 daddr,
                   unsigned short len,
                   unsigned short proto,
                   __wsum sum)
{
    return (__force __sum16)~from64to16(
        (__force u64)saddr + (__force u64)daddr +
        (__force u64)sum + ((len + proto) << 8));
}

__wsum csum_tcpudp_nofold(__be32 saddr, __be32 daddr,
                   unsigned short len,
                   unsigned short proto,
                   __wsum sum)
{
    unsigned long result;

    result = (__force u64)saddr + (__force u64)daddr +
         (__force u64)sum + ((len + proto) << 8);

    /* Fold down to 32-bits so we don't lose in the typedef-less 
       network stack.  */
    /* 64 to 33 */
    result = (result & 0xffffffff) + (result >> 32);
    /* 33 to 32 */
    result = (result & 0xffffffff) + (result >> 32);
    return (__force __wsum)result;
}
EXPORT_SYMBOL(csum_tcpudp_nofold);

/*
 * Do a 64-bit checksum on an arbitrary memory area..
 *
 * This isn't a great routine, but it's not _horrible_ either. The
 * inner loop could be unrolled a bit further, and there are better
 * ways to do the carry, but this is reasonable.
 */
static inline 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 = *buff << 8;
        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) {
            if (4 & (unsigned long) buff) {
                result += *(unsigned int *) buff;
                count--;
                len -= 4;
                buff += 4;
            }
            count >>= 1;    /* nr of 64-bit words.. */
            if (count) {
                unsigned long carry = 0;
                do {
                    unsigned long w = *(unsigned long *) buff;
                    count--;
                    buff += 8;
                    result += carry;
                    result += w;
                    carry = (w > result);
                } while (count);
                result += carry;
                result = (result & 0xffffffff) + (result >> 32);
            }
            if (len & 4) {
                result += *(unsigned int *) buff;
                buff += 4;
            }
        }
        if (len & 2) {
            result += *(unsigned short *) buff;
            buff += 2;
        }
    }
    if (len & 1)
        result += *buff;
    result = from64to16(result);
    if (odd)
        result = ((result >> 8) & 0xff) | ((result & 0xff) << 8);
out:
    return result;
}

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

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

    /* add in old sum, and carry.. */
    result += (__force u32)sum;
    /* 32+c bits -> 32 bits */
    result = (result & 0xffffffff) + (result >> 32);
    return (__force __wsum)result;
}

EXPORT_SYMBOL(csum_partial);

/*
 * this routine is used for miscellaneous IP-like checksums, mainly
 * in icmp.c
 */
__sum16 ip_compute_csum(const void *buff, int len)
{
    return (__force __sum16)~from64to16(do_csum(buff,len));
}