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.
6 * IP/TCP/UDP checksumming routines
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
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.
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.
31 /* Revised by Kenneth Albanowski for m68knommu. Basic problem: unaligned access kills, so most
32 of the assembly has to go. */
34 #include <net/checksum.h>
36 static inline unsigned short from32to16(unsigned long x
)
38 /* add up 16-bit and 16-bit for 16+c bit */
39 x
= (x
& 0xffff) + (x
>> 16);
41 x
= (x
& 0xffff) + (x
>> 16);
45 static unsigned long do_csum(const unsigned char * buff
, int len
)
48 unsigned long result
= 0;
52 odd
= 1 & (unsigned long) buff
;
58 count
= len
>> 1; /* nr of 16-bit words.. */
60 if (2 & (unsigned long) buff
) {
61 result
+= *(unsigned short *) buff
;
66 count
>>= 1; /* nr of 32-bit words.. */
68 unsigned long carry
= 0;
70 unsigned long w
= *(unsigned long *) buff
;
78 result
= (result
& 0xffff) + (result
>> 16);
81 result
+= *(unsigned short *) buff
;
86 result
+= (*buff
<< 8);
87 result
= from32to16(result
);
89 result
= ((result
>> 8) & 0xff) | ((result
& 0xff) << 8);
95 * This is a version of ip_compute_csum() optimized for IP headers,
96 * which always checksum on 4 octet boundaries.
98 unsigned short ip_fast_csum(unsigned char * iph
, unsigned int ihl
)
100 return ~do_csum(iph
,ihl
*4);
104 * computes the checksum of a memory block at buff, length len,
105 * and adds in "sum" (32-bit)
107 * returns a 32-bit number suitable for feeding into itself
108 * or csum_tcpudp_magic
110 * this function must be called with even lengths, except
111 * for the last fragment, which may be odd
113 * it's best to have buff aligned on a 32-bit boundary
115 unsigned int csum_partial(const unsigned char * buff
, int len
, unsigned int sum
)
117 unsigned int result
= do_csum(buff
, len
);
119 /* add in old sum, and carry.. */
126 EXPORT_SYMBOL(csum_partial
);
129 * this routine is used for miscellaneous IP-like checksums, mainly
132 unsigned short ip_compute_csum(const unsigned char * buff
, int len
)
134 return ~do_csum(buff
,len
);
138 * copy from fs while checksumming, otherwise like csum_partial
142 csum_partial_copy_from_user(const char *src
, char *dst
, int len
, int sum
, int *csum_err
)
144 if (csum_err
) *csum_err
= 0;
145 memcpy(dst
, src
, len
);
146 return csum_partial(dst
, len
, sum
);
150 * copy from ds while checksumming, otherwise like csum_partial
154 csum_partial_copy(const char *src
, char *dst
, int len
, int sum
)
156 memcpy(dst
, src
, len
);
157 return csum_partial(dst
, len
, sum
);