LXR linux/lib/checksum.c

   1/*
   2 *
   3 * INET         An implementation of the TCP/IP protocol suite for the LINUX
   4 *              operating system.  INET is implemented using the  BSD Socket
   5 *              interface as the means of communication with the user level.
   6 *
   7 *              IP/TCP/UDP checksumming routines
   8 *
   9 * Authors:     Jorge Cwik, <jorge@laser.satlink.net>
  10 *              Arnt Gulbrandsen, <agulbra@nvg.unit.no>
  11 *              Tom May, <ftom@netcom.com>
  12 *              Andreas Schwab, <schwab@issan.informatik.uni-dortmund.de>
  13 *              Lots of code moved from tcp.c and ip.c; see those files
  14 *              for more names.
  15 *
  16 * 03/02/96     Jes Sorensen, Andreas Schwab, Roman Hodek:
  17 *              Fixed some nasty bugs, causing some horrible crashes.
  18 *              A: At some points, the sum (%0) was used as
  19 *              length-counter instead of the length counter
  20 *              (%1). Thanks to Roman Hodek for pointing this out.
  21 *              B: GCC seems to mess up if one uses too many
  22 *              data-registers to hold input values and one tries to
  23 *              specify d0 and d1 as scratch registers. Letting gcc
  24 *              choose these registers itself solves the problem.
  25 *
  26 *              This program is free software; you can redistribute it and/or
  27 *              modify it under the terms of the GNU General Public License
  28 *              as published by the Free Software Foundation; either version
  29 *              2 of the License, or (at your option) any later version.
  30 */
  31
  32/* Revised by Kenneth Albanowski for m68knommu. Basic problem: unaligned access
  33 kills, so most of the assembly has to go. */
  34
  35#include <linux/module.h>
  36#include <net/checksum.h>
  37
  38#include <asm/byteorder.h>
  39
  40#ifndef do_csum
  41static inline unsigned short from32to16(unsigned int x)
  42{
  43        /* add up 16-bit and 16-bit for 16+c bit */
  44        x = (x & 0xffff) + (x >> 16);
  45        /* add up carry.. */
  46        x = (x & 0xffff) + (x >> 16);
  47        return x;
  48}
  49
  50static unsigned int do_csum(const unsigned char *buff, int len)
  51{
  52        int odd, count;
  53        unsigned int result = 0;
  54
  55        if (len <= 0)
  56                goto out;
  57        odd = 1 & (unsigned long) buff;
  58        if (odd) {
  59#ifdef __LITTLE_ENDIAN
  60                result += (*buff << 8);
  61#else
  62                result = *buff;
  63#endif
  64                len--;
  65                buff++;
  66        }
  67        count = len >> 1;               /* nr of 16-bit words.. */
  68        if (count) {
  69                if (2 & (unsigned long) buff) {
  70                        result += *(unsigned short *) buff;
  71                        count--;
  72                        len -= 2;
  73                        buff += 2;
  74                }
  75                count >>= 1;            /* nr of 32-bit words.. */
  76                if (count) {
  77                        unsigned int carry = 0;
  78                        do {
  79                                unsigned int w = *(unsigned int *) buff;
  80                                count--;
  81                                buff += 4;
  82                                result += carry;
  83                                result += w;
  84                                carry = (w > result);
  85                        } while (count);
  86                        result += carry;
  87                        result = (result & 0xffff) + (result >> 16);
  88                }
  89                if (len & 2) {
  90                        result += *(unsigned short *) buff;
  91                        buff += 2;
  92                }
  93        }
  94        if (len & 1)
  95#ifdef __LITTLE_ENDIAN
  96                result += *buff;
  97#else
  98                result += (*buff << 8);
  99#endif
 100        result = from32to16(result);
 101        if (odd)
 102                result = ((result >> 8) & 0xff) | ((result & 0xff) << 8);
 103out:
 104        return result;
 105}
 106#endif
 107
 108/*
 109 *      This is a version of ip_compute_csum() optimized for IP headers,
 110 *      which always checksum on 4 octet boundaries.
 111 */
 112__sum16 ip_fast_csum(const void *iph, unsigned int ihl)
 113{
 114        return (__force __sum16)~do_csum(iph, ihl*4);
 115}
 116EXPORT_SYMBOL(ip_fast_csum);
 117
 118/*
 119 * computes the checksum of a memory block at buff, length len,
 120 * and adds in "sum" (32-bit)
 121 *
 122 * returns a 32-bit number suitable for feeding into itself
 123 * or csum_tcpudp_magic
 124 *
 125 * this function must be called with even lengths, except
 126 * for the last fragment, which may be odd
 127 *
 128 * it's best to have buff aligned on a 32-bit boundary
 129 */
 130__wsum csum_partial(const void *buff, int len, __wsum wsum)
 131{
 132        unsigned int sum = (__force unsigned int)wsum;
 133        unsigned int result = do_csum(buff, len);
 134
 135        /* add in old sum, and carry.. */
 136        result += sum;
 137        if (sum > result)
 138                result += 1;
 139        return (__force __wsum)result;
 140}
 141EXPORT_SYMBOL(csum_partial);
 142
 143/*
 144 * this routine is used for miscellaneous IP-like checksums, mainly
 145 * in icmp.c
 146 */
 147__sum16 ip_compute_csum(const void *buff, int len)
 148{
 149        return (__force __sum16)~do_csum(buff, len);
 150}
 151EXPORT_SYMBOL(ip_compute_csum);
 152
 153/*
 154 * copy from fs while checksumming, otherwise like csum_partial
 155 */
 156__wsum
 157csum_partial_copy_from_user(const void __user *src, void *dst, int len,
 158                                                __wsum sum, int *csum_err)
 159{
 160        int missing;
 161
 162        missing = __copy_from_user(dst, src, len);
 163        if (missing) {
 164                memset(dst + len - missing, 0, missing);
 165                *csum_err = -EFAULT;
 166        } else
 167                *csum_err = 0;
 168
 169        return csum_partial(dst, len, sum);
 170}
 171EXPORT_SYMBOL(csum_partial_copy_from_user);
 172
 173/*
 174 * copy from ds while checksumming, otherwise like csum_partial
 175 */
 176__wsum
 177csum_partial_copy(const void *src, void *dst, int len, __wsum sum)
 178{
 179        memcpy(dst, src, len);
 180        return csum_partial(dst, len, sum);
 181}
 182EXPORT_SYMBOL(csum_partial_copy);
 183
 184#ifndef csum_tcpudp_nofold
 185__wsum csum_tcpudp_nofold(__be32 saddr, __be32 daddr,
 186                        unsigned short len,
 187                        unsigned short proto,
 188                        __wsum sum)
 189{
 190        unsigned long long s = (__force u32)sum;
 191
 192        s += (__force u32)saddr;
 193        s += (__force u32)daddr;
 194#ifdef __BIG_ENDIAN
 195        s += proto + len;
 196#else
 197        s += (proto + len) << 8;
 198#endif
 199        s += (s >> 32);
 200        return (__force __wsum)s;
 201}
 202EXPORT_SYMBOL(csum_tcpudp_nofold);
 203#endif
 204