arch/m68knommu/lib/checksum.c

   1 /*
   2  * INET         An implementation of the TCP/IP protocol suite for the LINUX
   3  *              operating system.  INET is implemented using the  BSD Socket
   4  *              interface as the means of communication with the user level.
   5  *
   6  *              IP/TCP/UDP checksumming routines
   7  *
   8  * Authors:     Jorge Cwik, <jorge@laser.satlink.net>
   9  *              Arnt Gulbrandsen, <agulbra@nvg.unit.no>
  10  *              Tom May, <ftom@netcom.com>
  11  *              Andreas Schwab, <schwab@issan.informatik.uni-dortmund.de>
  12  *              Lots of code moved from tcp.c and ip.c; see those files
  13  *              for more names.
  14  *
  15  * 03/02/96     Jes Sorensen, Andreas Schwab, Roman Hodek:
  16  *              Fixed some nasty bugs, causing some horrible crashes.
  17  *              A: At some points, the sum (%0) was used as
  18  *              length-counter instead of the length counter
  19  *              (%1). Thanks to Roman Hodek for pointing this out.
  20  *              B: GCC seems to mess up if one uses too many
  21  *              data-registers to hold input values and one tries to
  22  *              specify d0 and d1 as scratch registers. Letting gcc choose these
  23  *      registers itself solves the problem.
  24  *
  25  *              This program is free software; you can redistribute it and/or
  26  *              modify it under the terms of the GNU General Public License
  27  *              as published by the Free Software Foundation; either version
  28  *              2 of the License, or (at your option) any later version.
  29  */
  30
  31 /* Revised by Kenneth Albanowski for m68knommu. Basic problem: unaligned access kills, so most
  32    of the assembly has to go. */
  33
  34 #include <net/checksum.h>
  35
  36 static inline unsigned short from32to16(unsigned long x)
  37 {
  38         /* add up 16-bit and 16-bit for 16+c bit */
  39         x = (x & 0xffff) + (x >> 16);
  40         /* add up carry.. */
  41         x = (x & 0xffff) + (x >> 16);
  42         return x;
  43 }
  44
  45 static unsigned long do_csum(const unsigned char * buff, int len)
  46 {
  47         int odd, count;
  48         unsigned long result = 0;
  49
  50         if (len <= 0)
  51                 goto out;
  52         odd = 1 & (unsigned long) buff;
  53         if (odd) {
  54                 result = *buff;
  55                 len--;
  56                 buff++;
  57         }
  58         count = len >> 1;               /* nr of 16-bit words.. */
  59         if (count) {
  60                 if (2 & (unsigned long) buff) {
  61                         result += *(unsigned short *) buff;
  62                         count--;
  63                         len -= 2;
  64                         buff += 2;
  65                 }
  66                 count >>= 1;            /* nr of 32-bit words.. */
  67                 if (count) {
  68                         unsigned long carry = 0;
  69                         do {
  70                                 unsigned long w = *(unsigned long *) buff;
  71                                 count--;
  72                                 buff += 4;
  73                                 result += carry;
  74                                 result += w;
  75                                 carry = (w > result);
  76                         } while (count);
  77                         result += carry;
  78                         result = (result & 0xffff) + (result >> 16);
  79                 }
  80                 if (len & 2) {
  81                         result += *(unsigned short *) buff;
  82                         buff += 2;
  83                 }
  84         }
  85         if (len & 1)
  86                 result += (*buff << 8);
  87         result = from32to16(result);
  88         if (odd)
  89                 result = ((result >> 8) & 0xff) | ((result & 0xff) << 8);
  90 out:
  91         return result;
  92 }
  93
  94 /*
  95  *      This is a version of ip_compute_csum() optimized for IP headers,
  96  *      which always checksum on 4 octet boundaries.
  97  */
  98 unsigned short ip_fast_csum(unsigned char * iph, unsigned int ihl)
  99 {
 100         return ~do_csum(iph,ihl*4);
 101 }
 102
 103 /*
 104  * computes the checksum of a memory block at buff, length len,
 105  * and adds in "sum" (32-bit)
 106  *
 107  * returns a 32-bit number suitable for feeding into itself
 108  * or csum_tcpudp_magic
 109  *
 110  * this function must be called with even lengths, except
 111  * for the last fragment, which may be odd
 112  *
 113  * it's best to have buff aligned on a 32-bit boundary
 114  */
 115 unsigned int csum_partial(const unsigned char * buff, int len, unsigned int sum)
 116 {
 117         unsigned int result = do_csum(buff, len);
 118
 119         /* add in old sum, and carry.. */
 120         result += sum;
 121         if (sum > result)
 122                 result += 1;
 123         return result;
 124 }
 125
 126 EXPORT_SYMBOL(csum_partial);
 127
 128 /*
 129  * this routine is used for miscellaneous IP-like checksums, mainly
 130  * in icmp.c
 131  */
 132 unsigned short ip_compute_csum(const unsigned char * buff, int len)
 133 {
 134         return ~do_csum(buff,len);
 135 }
 136
 137 /*
 138  * copy from fs while checksumming, otherwise like csum_partial
 139  */
 140
 141 unsigned int
 142 csum_partial_copy_from_user(const char *src, char *dst, int len, int sum, int *csum_err)
 143 {
 144         if (csum_err) *csum_err = 0;
 145         memcpy(dst, src, len);
 146         return csum_partial(dst, len, sum);
 147 }
 148
 149 /*
 150  * copy from ds while checksumming, otherwise like csum_partial
 151  */
 152
 153 unsigned int
 154 csum_partial_copy(const char *src, char *dst, int len, int sum)
 155 {
 156         memcpy(dst, src, len);
 157         return csum_partial(dst, len, sum);
 158 }