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Linux/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/export.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 #ifndef ip_fast_csum
106 /*
107  *      This is a version of ip_compute_csum() optimized for IP headers,
108  *      which always checksum on 4 octet boundaries.
109  */
110 __sum16 ip_fast_csum(const void *iph, unsigned int ihl)
111 {
112         return (__force __sum16)~do_csum(iph, ihl*4);
113 }
114 EXPORT_SYMBOL(ip_fast_csum);
115 #endif
116 
117 /*
118  * computes the checksum of a memory block at buff, length len,
119  * and adds in "sum" (32-bit)
120  *
121  * returns a 32-bit number suitable for feeding into itself
122  * or csum_tcpudp_magic
123  *
124  * this function must be called with even lengths, except
125  * for the last fragment, which may be odd
126  *
127  * it's best to have buff aligned on a 32-bit boundary
128  */
129 __wsum csum_partial(const void *buff, int len, __wsum wsum)
130 {
131         unsigned int sum = (__force unsigned int)wsum;
132         unsigned int result = do_csum(buff, len);
133 
134         /* add in old sum, and carry.. */
135         result += sum;
136         if (sum > result)
137                 result += 1;
138         return (__force __wsum)result;
139 }
140 EXPORT_SYMBOL(csum_partial);
141 
142 /*
143  * this routine is used for miscellaneous IP-like checksums, mainly
144  * in icmp.c
145  */
146 __sum16 ip_compute_csum(const void *buff, int len)
147 {
148         return (__force __sum16)~do_csum(buff, len);
149 }
150 EXPORT_SYMBOL(ip_compute_csum);
151 
152 /*
153  * copy from fs while checksumming, otherwise like csum_partial
154  */
155 __wsum
156 csum_partial_copy_from_user(const void __user *src, void *dst, int len,
157                                                 __wsum sum, int *csum_err)
158 {
159         int missing;
160 
161         missing = __copy_from_user(dst, src, len);
162         if (missing) {
163                 memset(dst + len - missing, 0, missing);
164                 *csum_err = -EFAULT;
165         } else
166                 *csum_err = 0;
167 
168         return csum_partial(dst, len, sum);
169 }
170 EXPORT_SYMBOL(csum_partial_copy_from_user);
171 
172 /*
173  * copy from ds while checksumming, otherwise like csum_partial
174  */
175 __wsum
176 csum_partial_copy(const void *src, void *dst, int len, __wsum sum)
177 {
178         memcpy(dst, src, len);
179         return csum_partial(dst, len, sum);
180 }
181 EXPORT_SYMBOL(csum_partial_copy);
182 
183 #ifndef csum_tcpudp_nofold
184 static inline u32 from64to32(u64 x)
185 {
186         /* add up 32-bit and 32-bit for 32+c bit */
187         x = (x & 0xffffffff) + (x >> 32);
188         /* add up carry.. */
189         x = (x & 0xffffffff) + (x >> 32);
190         return (u32)x;
191 }
192 
193 __wsum csum_tcpudp_nofold(__be32 saddr, __be32 daddr,
194                           __u32 len, __u8 proto, __wsum sum)
195 {
196         unsigned long long s = (__force u32)sum;
197 
198         s += (__force u32)saddr;
199         s += (__force u32)daddr;
200 #ifdef __BIG_ENDIAN
201         s += proto + len;
202 #else
203         s += (proto + len) << 8;
204 #endif
205         return (__force __wsum)from64to32(s);
206 }
207 EXPORT_SYMBOL(csum_tcpudp_nofold);
208 #endif
209 

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