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 <linux/module.h>
  35 #include <net/checksum.h>
  36
  37 static inline unsigned short from32to16(unsigned long x)
  38 {
  39         /* add up 16-bit and 16-bit for 16+c bit */
  40         x = (x & 0xffff) + (x >> 16);
  41         /* add up carry.. */
  42         x = (x & 0xffff) + (x >> 16);
  43         return x;
  44 }
  45
  46 static unsigned long do_csum(const unsigned char * buff, int len)
  47 {
  48         int odd, count;
  49         unsigned long result = 0;
  50
  51         if (len <= 0)
  52                 goto out;
  53         odd = 1 & (unsigned long) buff;
  54         if (odd) {
  55                 result = *buff;
  56                 len--;
  57                 buff++;
  58         }
  59         count = len >> 1;               /* nr of 16-bit words.. */
  60         if (count) {
  61                 if (2 & (unsigned long) buff) {
  62                         result += *(unsigned short *) buff;
  63                         count--;
  64                         len -= 2;
  65                         buff += 2;
  66                 }
  67                 count >>= 1;            /* nr of 32-bit words.. */
  68                 if (count) {
  69                         unsigned long carry = 0;
  70                         do {
  71                                 unsigned long w = *(unsigned long *) buff;
  72                                 count--;
  73                                 buff += 4;
  74                                 result += carry;
  75                                 result += w;
  76                                 carry = (w > result);
  77                         } while (count);
  78                         result += carry;
  79                         result = (result & 0xffff) + (result >> 16);
  80                 }
  81                 if (len & 2) {
  82                         result += *(unsigned short *) buff;
  83                         buff += 2;
  84                 }
  85         }
  86         if (len & 1)
  87                 result += (*buff << 8);
  88         result = from32to16(result);
  89         if (odd)
  90                 result = ((result >> 8) & 0xff) | ((result & 0xff) << 8);
  91 out:
  92         return result;
  93 }
  94
  95 /*
  96  *      This is a version of ip_compute_csum() optimized for IP headers,
  97  *      which always checksum on 4 octet boundaries.
  98  */
  99 __sum16 ip_fast_csum(const void *iph, unsigned int ihl)
 100 {
 101         return (__force __sum16)~do_csum(iph,ihl*4);
 102 }
 103
 104 /*
 105  * computes the checksum of a memory block at buff, length len,
 106  * and adds in "sum" (32-bit)
 107  *
 108  * returns a 32-bit number suitable for feeding into itself
 109  * or csum_tcpudp_magic
 110  *
 111  * this function must be called with even lengths, except
 112  * for the last fragment, which may be odd
 113  *
 114  * it's best to have buff aligned on a 32-bit boundary
 115  */
 116 __wsum csum_partial(const void *buff, int len, __wsum sum)
 117 {
 118         unsigned int result = do_csum(buff, len);
 119
 120         /* add in old sum, and carry.. */
 121         result += (__force u32)sum;
 122         if ((__force u32)sum > result)
 123                 result += 1;
 124         return (__force __wsum)result;
 125 }
 126
 127 EXPORT_SYMBOL(csum_partial);
 128
 129 /*
 130  * this routine is used for miscellaneous IP-like checksums, mainly
 131  * in icmp.c
 132  */
 133 __sum16 ip_compute_csum(const void *buff, int len)
 134 {
 135         return (__force __sum16)~do_csum(buff,len);
 136 }
 137
 138 /*
 139  * copy from fs while checksumming, otherwise like csum_partial
 140  */
 141
 142 __wsum
 143 csum_partial_copy_from_user(const void __user *src, void *dst,
 144                             int len, __wsum sum, int *csum_err)
 145 {
 146         if (csum_err) *csum_err = 0;
 147         memcpy(dst, (__force const void *)src, len);
 148         return csum_partial(dst, len, sum);
 149 }
 150
 151 /*
 152  * copy from ds while checksumming, otherwise like csum_partial
 153  */
 154
 155 __wsum
 156 csum_partial_copy_nocheck(const void *src, void *dst, int len, __wsum sum)
 157 {
 158         memcpy(dst, src, len);
 159         return csum_partial(dst, len, sum);
 160 }