linux/lib/checksum.c
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   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
  40static inline unsigned short from32to16(unsigned long x)
  41{
  42        /* add up 16-bit and 16-bit for 16+c bit */
  43        x = (x & 0xffff) + (x >> 16);
  44        /* add up carry.. */
  45        x = (x & 0xffff) + (x >> 16);
  46        return x;
  47}
  48
  49static unsigned int do_csum(const unsigned char *buff, int len)
  50{
  51        int odd, count;
  52        unsigned long result = 0;
  53
  54        if (len <= 0)
  55                goto out;
  56        odd = 1 & (unsigned long) buff;
  57        if (odd) {
  58#ifdef __LITTLE_ENDIAN
  59                result = *buff;
  60#else
  61                result += (*buff << 8);
  62#endif
  63                len--;
  64                buff++;
  65        }
  66        count = len >> 1;               /* nr of 16-bit words.. */
  67        if (count) {
  68                if (2 & (unsigned long) buff) {
  69                        result += *(unsigned short *) buff;
  70                        count--;
  71                        len -= 2;
  72                        buff += 2;
  73                }
  74                count >>= 1;            /* nr of 32-bit words.. */
  75                if (count) {
  76                        unsigned long carry = 0;
  77                        do {
  78                                unsigned long w = *(unsigned int *) buff;
  79                                count--;
  80                                buff += 4;
  81                                result += carry;
  82                                result += w;
  83                                carry = (w > result);
  84                        } while (count);
  85                        result += carry;
  86                        result = (result & 0xffff) + (result >> 16);
  87                }
  88                if (len & 2) {
  89                        result += *(unsigned short *) buff;
  90                        buff += 2;
  91                }
  92        }
  93        if (len & 1)
  94#ifdef __LITTLE_ENDIAN
  95                result += *buff;
  96#else
  97                result += (*buff << 8);
  98#endif
  99        result = from32to16(result);
 100        if (odd)
 101                result = ((result >> 8) & 0xff) | ((result & 0xff) << 8);
 102out:
 103        return result;
 104}
 105
 106/*
 107 *      This is a version of ip_compute_csum() optimized for IP headers,
 108 *      which always checksum on 4 octet boundaries.
 109 */
 110__sum16 ip_fast_csum(const void *iph, unsigned int ihl)
 111{
 112        return (__force __sum16)~do_csum(iph, ihl*4);
 113}
 114EXPORT_SYMBOL(ip_fast_csum);
 115
 116/*
 117 * computes the checksum of a memory block at buff, length len,
 118 * and adds in "sum" (32-bit)
 119 *
 120 * returns a 32-bit number suitable for feeding into itself
 121 * or csum_tcpudp_magic
 122 *
 123 * this function must be called with even lengths, except
 124 * for the last fragment, which may be odd
 125 *
 126 * it's best to have buff aligned on a 32-bit boundary
 127 */
 128__wsum csum_partial(const void *buff, int len, __wsum wsum)
 129{
 130        unsigned int sum = (__force unsigned int)wsum;
 131        unsigned int result = do_csum(buff, len);
 132
 133        /* add in old sum, and carry.. */
 134        result += sum;
 135        if (sum > result)
 136                result += 1;
 137        return (__force __wsum)result;
 138}
 139EXPORT_SYMBOL(csum_partial);
 140
 141/*
 142 * this routine is used for miscellaneous IP-like checksums, mainly
 143 * in icmp.c
 144 */
 145__sum16 ip_compute_csum(const void *buff, int len)
 146{
 147        return (__force __sum16)~do_csum(buff, len);
 148}
 149EXPORT_SYMBOL(ip_compute_csum);
 150
 151/*
 152 * copy from fs while checksumming, otherwise like csum_partial
 153 */
 154__wsum
 155csum_partial_copy_from_user(const void __user *src, void *dst, int len,
 156                                                __wsum sum, int *csum_err)
 157{
 158        int missing;
 159
 160        missing = __copy_from_user(dst, src, len);
 161        if (missing) {
 162                memset(dst + len - missing, 0, missing);
 163                *csum_err = -EFAULT;
 164        } else
 165                *csum_err = 0;
 166
 167        return csum_partial(dst, len, sum);
 168}
 169EXPORT_SYMBOL(csum_partial_copy_from_user);
 170
 171/*
 172 * copy from ds while checksumming, otherwise like csum_partial
 173 */
 174__wsum
 175csum_partial_copy(const void *src, void *dst, int len, __wsum sum)
 176{
 177        memcpy(dst, src, len);
 178        return csum_partial(dst, len, sum);
 179}
 180EXPORT_SYMBOL(csum_partial_copy);
 181
 182#ifndef csum_tcpudp_nofold
 183__wsum csum_tcpudp_nofold(__be32 saddr, __be32 daddr,
 184                        unsigned short len,
 185                        unsigned short proto,
 186                        __wsum sum)
 187{
 188        unsigned long long s = (__force u32)sum;
 189
 190        s += (__force u32)saddr;
 191        s += (__force u32)daddr;
 192#ifdef __BIG_ENDIAN
 193        s += proto + len;
 194#else
 195        s += (proto + len) << 8;
 196#endif
 197        s += (s >> 32);
 198        return (__force __wsum)s;
 199}
 200EXPORT_SYMBOL(csum_tcpudp_nofold);
 201#endif
 202