arch/metag/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 int 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;
  52         unsigned int result = 0;
  53
  54         if (len <= 0)
  55                 goto out;
  56         odd = 1 & (unsigned long) buff;
  57         if (odd) {
  58 #ifdef __LITTLE_ENDIAN
  59                 result += (*buff << 8);
  60 #else
  61                 result = *buff;
  62 #endif
  63                 len--;
  64                 buff++;
  65         }
  66         if (len >= 2) {
  67                 if (2 & (unsigned long) buff) {
  68                         result += *(unsigned short *) buff;
  69                         len -= 2;
  70                         buff += 2;
  71                 }
  72                 if (len >= 4) {
  73                         const unsigned char *end = buff + ((unsigned)len & ~3);
  74                         unsigned int carry = 0;
  75                         do {
  76                                 unsigned int w = *(unsigned int *) buff;
  77                                 buff += 4;
  78                                 result += carry;
  79                                 result += w;
  80                                 carry = (w > result);
  81                         } while (buff < end);
  82                         result += carry;
  83                         result = (result & 0xffff) + (result >> 16);
  84                 }
  85                 if (len & 2) {
  86                         result += *(unsigned short *) buff;
  87                         buff += 2;
  88                 }
  89         }
  90         if (len & 1)
  91 #ifdef __LITTLE_ENDIAN
  92                 result += *buff;
  93 #else
  94                 result += (*buff << 8);
  95 #endif
  96         result = from32to16(result);
  97         if (odd)
  98                 result = ((result >> 8) & 0xff) | ((result & 0xff) << 8);
  99 out:
 100         return result;
 101 }
 102 EXPORT_SYMBOL(ip_fast_csum);
 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 wsum)
 117 {
 118         unsigned int sum = (__force unsigned int)wsum;
 119         unsigned int result = do_csum(buff, len);
 120
 121         /* add in old sum, and carry.. */
 122         result += sum;
 123         if (sum > result)
 124                 result += 1;
 125         return (__force __wsum)result;
 126 }
 127
 128 /*
 129  * this routine is used for miscellaneous IP-like checksums, mainly
 130  * in icmp.c
 131  */
 132 __sum16 ip_compute_csum(const void *buff, int len)
 133 {
 134         return (__force __sum16)~do_csum(buff, len);
 135 }
 136 EXPORT_SYMBOL(ip_compute_csum);
 137
 138 /*
 139  * copy from fs while checksumming, otherwise like csum_partial
 140  */
 141 __wsum
 142 csum_partial_copy_from_user(const void __user *src, void *dst, int len,
 143                                                 __wsum sum, int *csum_err)
 144 {
 145         int missing;
 146
 147         missing = __copy_from_user(dst, src, len);
 148         if (missing) {
 149                 memset(dst + len - missing, 0, missing);
 150                 *csum_err = -EFAULT;
 151         } else
 152                 *csum_err = 0;
 153
 154         return csum_partial(dst, len, sum);
 155 }
 156 EXPORT_SYMBOL(csum_partial_copy_from_user);
 157
 158 /*
 159  * copy from ds while checksumming, otherwise like csum_partial
 160  */
 161 __wsum
 162 csum_partial_copy(const void *src, void *dst, int len, __wsum sum)
 163 {
 164         memcpy(dst, src, len);
 165         return csum_partial(dst, len, sum);
 166 }
 167 EXPORT_SYMBOL(csum_partial_copy);