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
  41 static 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
  50 static 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);
 103 out:
 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 }
 116 EXPORT_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 }
 141 EXPORT_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 }
 151 EXPORT_SYMBOL(ip_compute_csum);
 152
 153 /*
 154  * copy from fs while checksumming, otherwise like csum_partial
 155  */
 156 __wsum
 157 csum_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 }
 171 EXPORT_SYMBOL(csum_partial_copy_from_user);
 172
 173 /*
 174  * copy from ds while checksumming, otherwise like csum_partial
 175  */
 176 __wsum
 177 csum_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 }
 182 EXPORT_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 }
 202 EXPORT_SYMBOL(csum_tcpudp_nofold);
 203 #endif