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