tjh.dev
Linux kernel mirror (for testing)
git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git
kernel
os
linux
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#include <asm/checksum.h>
36
37static 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
46static 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);
91out:
92 return result;
93}
94
95/*
96 * computes the checksum of a memory block at buff, length len,
97 * and adds in "sum" (32-bit)
98 *
99 * returns a 32-bit number suitable for feeding into itself
100 * or csum_tcpudp_magic
101 *
102 * this function must be called with even lengths, except
103 * for the last fragment, which may be odd
104 *
105 * it's best to have buff aligned on a 32-bit boundary
106 */
107unsigned int csum_partial(const unsigned char * buff, int len, unsigned int sum)
108{
109 unsigned int result = do_csum(buff, len);
110
111 /* add in old sum, and carry.. */
112 result += sum;
113 if (sum > result)
114 result += 1;
115 return result;
116}
117
118/*
119 * this routine is used for miscellaneous IP-like checksums, mainly
120 * in icmp.c
121 */
122unsigned short ip_compute_csum(const unsigned char * buff, int len)
123{
124 return ~do_csum(buff,len);
125}
126
127/*
128 * copy from fs while checksumming, otherwise like csum_partial
129 */
130
131unsigned int
132csum_partial_copy_from_user(const char *src, char *dst, int len, int sum, int *csum_err)
133{
134 if (csum_err) *csum_err = 0;
135 memcpy(dst, src, len);
136 return csum_partial(dst, len, sum);
137}
138
139/*
140 * copy from ds while checksumming, otherwise like csum_partial
141 */
142
143unsigned int
144csum_partial_copy(const char *src, char *dst, int len, int sum)
145{
146 memcpy(dst, src, len);
147 return csum_partial(dst, len, sum);
148}