checksum.c

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/*
 * INET     An implementation of the TCP/IP protocol suite for the LINUX
 *      operating system.  INET is implemented using the  BSD Socket
 *      interface as the means of communication with the user level.
 *
 *      MIPS specific IP/TCP/UDP checksumming routines
 *
 * Authors: Ralf Baechle, <[email protected]>
 *      Lots of code moved from tcp.c and ip.c; see those files
 *      for more names.
 *
 *      This program is free software; you can redistribute it and/or
 *      modify it under the terms of the GNU General Public License
 *      as published by the Free Software Foundation; either version
 *      2 of the License, or (at your option) any later version.
 */
#include <linux/module.h>
#include <linux/types.h>

#include <net/checksum.h>
#include <asm/byteorder.h>
#include <asm/string.h>
#include <asm/uaccess.h>

#define addc(_t,_r)                     \
    __asm__ __volatile__ (          \
"       add             %0, %1, %0\n"   \
"       addc            %0, %%r0, %0\n" \
    : "=r"(_t)                      \
    : "r"(_r), "0"(_t));

static inline unsigned short from32to16(unsigned int x)
{
    /* 32 bits --> 16 bits + carry */
    x = (x & 0xffff) + (x >> 16);
    /* 16 bits + carry --> 16 bits including carry */
    x = (x & 0xffff) + (x >> 16);
    return (unsigned short)x;
}

static inline unsigned int do_csum(const unsigned char * buff, int len)
{
    int odd, count;
    unsigned int result = 0;

    if (len <= 0)
        goto out;
    odd = 1 & (unsigned long) buff;
    if (odd) {
        result = be16_to_cpu(*buff);
        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) {
            while (count >= 4) {
                unsigned int r1, r2, r3, r4;
                r1 = *(unsigned int *)(buff + 0);
                r2 = *(unsigned int *)(buff + 4);
                r3 = *(unsigned int *)(buff + 8);
                r4 = *(unsigned int *)(buff + 12);
                addc(result, r1);
                addc(result, r2);
                addc(result, r3);
                addc(result, r4);
                count -= 4;
                buff += 16;
            }
            while (count) {
                unsigned int w = *(unsigned int *) buff;
                count--;
                buff += 4;
                addc(result, w);
            }
            result = (result & 0xffff) + (result >> 16);
        }
        if (len & 2) {
            result += *(unsigned short *) buff;
            buff += 2;
        }
    }
    if (len & 1)
        result += le16_to_cpu(*buff);
    result = from32to16(result);
    if (odd)
        result = swab16(result);
out:
    return result;
}

/*
 * computes a partial checksum, e.g. for TCP/UDP fragments
 */
/*
 * why bother folding?
 */
__wsum csum_partial(const void *buff, int len, __wsum sum)
{
    unsigned int result = do_csum(buff, len);
    addc(result, sum);
    return (__force __wsum)from32to16(result);
}

EXPORT_SYMBOL(csum_partial);

/*
 * copy while checksumming, otherwise like csum_partial
 */
__wsum csum_partial_copy_nocheck(const void *src, void *dst,
                       int len, __wsum sum)
{
    /*
     * It's 2:30 am and I don't feel like doing it real ...
     * This is lots slower than the real thing (tm)
     */
    sum = csum_partial(src, len, sum);
    memcpy(dst, src, len);

    return sum;
}
EXPORT_SYMBOL(csum_partial_copy_nocheck);

/*
 * Copy from userspace and compute checksum.  If we catch an exception
 * then zero the rest of the buffer.
 */
__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);
}
EXPORT_SYMBOL(csum_partial_copy_from_user);