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/export.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;
  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        if (len >= 2) {
  68                if (2 & (unsigned long) buff) {
  69                        result += *(unsigned short *) buff;
  70                        len -= 2;
  71                        buff += 2;
  72                }
  73                if (len >= 4) {
  74                        const unsigned char *end = buff + ((unsigned)len & ~3);
  75                        unsigned int carry = 0;
  76                        do {
  77                                unsigned int w = *(unsigned int *) buff;
  78                                buff += 4;
  79                                result += carry;
  80                                result += w;
  81                                carry = (w > result);
  82                        } while (buff < end);
  83                        result += carry;
  84                        result = (result & 0xffff) + (result >> 16);
  85                }
  86                if (len & 2) {
  87                        result += *(unsigned short *) buff;
  88                        buff += 2;
  89                }
  90        }
  91        if (len & 1)
  92#ifdef __LITTLE_ENDIAN
  93                result += *buff;
  94#else
  95                result += (*buff << 8);
  96#endif
  97        result = from32to16(result);
  98        if (odd)
  99                result = ((result >> 8) & 0xff) | ((result & 0xff) << 8);
 100out:
 101        return result;
 102}
 103#endif
 104
 105#ifndef ip_fast_csum
 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#endif
 116
 117/*
 118 * computes the checksum of a memory block at buff, length len,
 119 * and adds in "sum" (32-bit)
 120 *
 121 * returns a 32-bit number suitable for feeding into itself
 122 * or csum_tcpudp_magic
 123 *
 124 * this function must be called with even lengths, except
 125 * for the last fragment, which may be odd
 126 *
 127 * it's best to have buff aligned on a 32-bit boundary
 128 */
 129__wsum csum_partial(const void *buff, int len, __wsum wsum)
 130{
 131        unsigned int sum = (__force unsigned int)wsum;
 132        unsigned int result = do_csum(buff, len);
 133
 134        /* add in old sum, and carry.. */
 135        result += sum;
 136        if (sum > result)
 137                result += 1;
 138        return (__force __wsum)result;
 139}
 140EXPORT_SYMBOL(csum_partial);
 141
 142/*
 143 * this routine is used for miscellaneous IP-like checksums, mainly
 144 * in icmp.c
 145 */
 146__sum16 ip_compute_csum(const void *buff, int len)
 147{
 148        return (__force __sum16)~do_csum(buff, len);
 149}
 150EXPORT_SYMBOL(ip_compute_csum);
 151
 152/*
 153 * copy from fs while checksumming, otherwise like csum_partial
 154 */
 155__wsum
 156csum_partial_copy_from_user(const void __user *src, void *dst, int len,
 157                                                __wsum sum, int *csum_err)
 158{
 159        int missing;
 160
 161        missing = __copy_from_user(dst, src, len);
 162        if (missing) {
 163                memset(dst + len - missing, 0, missing);
 164                *csum_err = -EFAULT;
 165        } else
 166                *csum_err = 0;
 167
 168        return csum_partial(dst, len, sum);
 169}
 170EXPORT_SYMBOL(csum_partial_copy_from_user);
 171
 172/*
 173 * copy from ds while checksumming, otherwise like csum_partial
 174 */
 175__wsum
 176csum_partial_copy(const void *src, void *dst, int len, __wsum sum)
 177{
 178        memcpy(dst, src, len);
 179        return csum_partial(dst, len, sum);
 180}
 181EXPORT_SYMBOL(csum_partial_copy);
 182
 183#ifndef csum_tcpudp_nofold
 184__wsum csum_tcpudp_nofold(__be32 saddr, __be32 daddr,
 185                          __u32 len, __u8 proto, __wsum sum)
 186{
 187        unsigned long long s = (__force u32)sum;
 188
 189        s += (__force u32)saddr;
 190        s += (__force u32)daddr;
 191#ifdef __BIG_ENDIAN
 192        s += proto + len;
 193#else
 194        s += (proto + len) << 8;
 195#endif
 196        s += (s >> 32);
 197        return (__force __wsum)s;
 198}
 199EXPORT_SYMBOL(csum_tcpudp_nofold);
 200#endif
 201