checksum.c

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/*
 * Copyright 2010 Tilera Corporation. All Rights Reserved.
 *
 *   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, version 2.
 *
 *   This program is distributed in the hope that it will be useful, but
 *   WITHOUT ANY WARRANTY; without even the implied warranty of
 *   MERCHANTABILITY OR FITNESS FOR A PARTICULAR PURPOSE, GOOD TITLE or
 *   NON INFRINGEMENT.  See the GNU General Public License for
 *   more details.
 * Support code for the main lib/checksum.c.
 */

#include <net/checksum.h>
#include <linux/module.h>

__wsum 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 += *(const unsigned short *)buff;
            count--;
            len -= 2;
            buff += 2;
        }
        count >>= 1;        /* nr of 32-bit words.. */
        if (count) {
#ifdef __tilegx__
            if (4 & (unsigned long) buff) {
                unsigned int w = *(const unsigned int *)buff;
                result = __insn_v2sadau(result, w, 0);
                count--;
                len -= 4;
                buff += 4;
            }
            count >>= 1;        /* nr of 64-bit words.. */
#endif

            /*
             * This algorithm could wrap around for very
             * large buffers, but those should be impossible.
             */
            BUG_ON(count >= 65530);

            while (count) {
                unsigned long w = *(const unsigned long *)buff;
                count--;
                buff += sizeof(w);
#ifdef __tilegx__
                result = __insn_v2sadau(result, w, 0);
#else
                result = __insn_sadah_u(result, w, 0);
#endif
            }
#ifdef __tilegx__
            if (len & 4) {
                unsigned int w = *(const unsigned int *)buff;
                result = __insn_v2sadau(result, w, 0);
                buff += 4;
            }
#endif
        }
        if (len & 2) {
            result += *(const unsigned short *) buff;
            buff += 2;
        }
    }
    if (len & 1)
        result += *buff;
    result = csum_long(result);
    if (odd)
        result = swab16(result);
out:
    return result;
}