csum_partial_copy.c

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/*
 * Network Checksum & Copy routine
 *
 * Copyright (C) 1999, 2003-2004 Hewlett-Packard Co
 *  Stephane Eranian <[email protected]>
 *
 * Most of the code has been imported from Linux/Alpha
 */

#include <linux/module.h>
#include <linux/types.h>
#include <linux/string.h>

#include <asm/uaccess.h>

/*
 * XXX Fixme: those 2 inlines are meant for debugging and will go away
 */
static inline unsigned
short from64to16(unsigned long x)
{
    /* add up 32-bit words for 33 bits */
    x = (x & 0xffffffff) + (x >> 32);
    /* add up 16-bit and 17-bit words for 17+c bits */
    x = (x & 0xffff) + (x >> 16);
    /* add up 16-bit and 2-bit for 16+c bit */
    x = (x & 0xffff) + (x >> 16);
    /* add up carry.. */
    x = (x & 0xffff) + (x >> 16);
    return x;
}

static inline
unsigned long do_csum_c(const unsigned char * buff, int len, unsigned int psum)
{
    int odd, count;
    unsigned long result = (unsigned long)psum;

    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;
}

/*
 * XXX Fixme
 *
 * This is very ugly but temporary. THIS NEEDS SERIOUS ENHANCEMENTS.
 * But it's very tricky to get right even in C.
 */
extern unsigned long do_csum(const unsigned char *, long);

__wsum
csum_partial_copy_from_user(const void __user *src, void *dst,
                int len, __wsum psum, int *errp)
{
    unsigned long result;

    /* XXX Fixme
     * for now we separate the copy from checksum for obvious
     * alignment difficulties. Look at the Alpha code and you'll be
     * scared.
     */

    if (__copy_from_user(dst, src, len) != 0 && errp)
        *errp = -EFAULT;

    result = do_csum(dst, len);

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

EXPORT_SYMBOL(csum_partial_copy_from_user);

__wsum
csum_partial_copy_nocheck(const void *src, void *dst, int len, __wsum sum)
{
    return csum_partial_copy_from_user((__force const void __user *)src,
                       dst, len, sum, NULL);
}

EXPORT_SYMBOL(csum_partial_copy_nocheck);