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;
  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);
 100 out:
 101         return result;
 102 }
 103 #endif
 104
 105 /*
 106  *      This is a version of ip_compute_csum() optimized for IP headers,
 107  *      which always checksum on 4 octet boundaries.
 108  */
 109 __sum16 ip_fast_csum(const void *iph, unsigned int ihl)
 110 {
 111         return (__force __sum16)~do_csum(iph, ihl*4);
 112 }
 113 EXPORT_SYMBOL(ip_fast_csum);
 114
 115 /*
 116  * computes the checksum of a memory block at buff, length len,
 117  * and adds in "sum" (32-bit)
 118  *
 119  * returns a 32-bit number suitable for feeding into itself
 120  * or csum_tcpudp_magic
 121  *
 122  * this function must be called with even lengths, except
 123  * for the last fragment, which may be odd
 124  *
 125  * it's best to have buff aligned on a 32-bit boundary
 126  */
 127 __wsum csum_partial(const void *buff, int len, __wsum wsum)
 128 {
 129         unsigned int sum = (__force unsigned int)wsum;
 130         unsigned int result = do_csum(buff, len);
 131
 132         /* add in old sum, and carry.. */
 133         result += sum;
 134         if (sum > result)
 135                 result += 1;
 136         return (__force __wsum)result;
 137 }
 138 EXPORT_SYMBOL(csum_partial);
 139
 140 /*
 141  * this routine is used for miscellaneous IP-like checksums, mainly
 142  * in icmp.c
 143  */
 144 __sum16 ip_compute_csum(const void *buff, int len)
 145 {
 146         return (__force __sum16)~do_csum(buff, len);
 147 }
 148 EXPORT_SYMBOL(ip_compute_csum);
 149
 150 /*
 151  * copy from fs while checksumming, otherwise like csum_partial
 152  */
 153 __wsum
 154 csum_partial_copy_from_user(const void __user *src, void *dst, int len,
 155                                                 __wsum sum, int *csum_err)
 156 {
 157         int missing;
 158
 159         missing = __copy_from_user(dst, src, len);
 160         if (missing) {
 161                 memset(dst + len - missing, 0, missing);
 162                 *csum_err = -EFAULT;
 163         } else
 164                 *csum_err = 0;
 165
 166         return csum_partial(dst, len, sum);
 167 }
 168 EXPORT_SYMBOL(csum_partial_copy_from_user);
 169
 170 /*
 171  * copy from ds while checksumming, otherwise like csum_partial
 172  */
 173 __wsum
 174 csum_partial_copy(const void *src, void *dst, int len, __wsum sum)
 175 {
 176         memcpy(dst, src, len);
 177         return csum_partial(dst, len, sum);
 178 }
 179 EXPORT_SYMBOL(csum_partial_copy);
 180
 181 #ifndef csum_tcpudp_nofold
 182 __wsum csum_tcpudp_nofold(__be32 saddr, __be32 daddr,
 183                         unsigned short len,
 184                         unsigned short proto,
 185                         __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 }
 199 EXPORT_SYMBOL(csum_tcpudp_nofold);
 200 #endif