Root/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#ifndef do_csum
41static 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
50static unsigned int do_csum(const unsigned char *buff, int len)
51{
52    int odd, count;
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    count = len >> 1; /* nr of 16-bit words.. */
68    if (count) {
69        if (2 & (unsigned long) buff) {
70            result += *(unsigned short *) buff;
71            count--;
72            len -= 2;
73            buff += 2;
74        }
75        count >>= 1; /* nr of 32-bit words.. */
76        if (count) {
77            unsigned int carry = 0;
78            do {
79                unsigned int w = *(unsigned int *) buff;
80                count--;
81                buff += 4;
82                result += carry;
83                result += w;
84                carry = (w > result);
85            } while (count);
86            result += carry;
87            result = (result & 0xffff) + (result >> 16);
88        }
89        if (len & 2) {
90            result += *(unsigned short *) buff;
91            buff += 2;
92        }
93    }
94    if (len & 1)
95#ifdef __LITTLE_ENDIAN
96        result += *buff;
97#else
98        result += (*buff << 8);
99#endif
100    result = from32to16(result);
101    if (odd)
102        result = ((result >> 8) & 0xff) | ((result & 0xff) << 8);
103out:
104    return result;
105}
106#endif
107
108/*
109 * This is a version of ip_compute_csum() optimized for IP headers,
110 * which always checksum on 4 octet boundaries.
111 */
112__sum16 ip_fast_csum(const void *iph, unsigned int ihl)
113{
114    return (__force __sum16)~do_csum(iph, ihl*4);
115}
116EXPORT_SYMBOL(ip_fast_csum);
117
118/*
119 * computes the checksum of a memory block at buff, length len,
120 * and adds in "sum" (32-bit)
121 *
122 * returns a 32-bit number suitable for feeding into itself
123 * or csum_tcpudp_magic
124 *
125 * this function must be called with even lengths, except
126 * for the last fragment, which may be odd
127 *
128 * it's best to have buff aligned on a 32-bit boundary
129 */
130__wsum csum_partial(const void *buff, int len, __wsum wsum)
131{
132    unsigned int sum = (__force unsigned int)wsum;
133    unsigned int result = do_csum(buff, len);
134
135    /* add in old sum, and carry.. */
136    result += sum;
137    if (sum > result)
138        result += 1;
139    return (__force __wsum)result;
140}
141EXPORT_SYMBOL(csum_partial);
142
143/*
144 * this routine is used for miscellaneous IP-like checksums, mainly
145 * in icmp.c
146 */
147__sum16 ip_compute_csum(const void *buff, int len)
148{
149    return (__force __sum16)~do_csum(buff, len);
150}
151EXPORT_SYMBOL(ip_compute_csum);
152
153/*
154 * copy from fs while checksumming, otherwise like csum_partial
155 */
156__wsum
157csum_partial_copy_from_user(const void __user *src, void *dst, int len,
158                        __wsum sum, int *csum_err)
159{
160    int missing;
161
162    missing = __copy_from_user(dst, src, len);
163    if (missing) {
164        memset(dst + len - missing, 0, missing);
165        *csum_err = -EFAULT;
166    } else
167        *csum_err = 0;
168
169    return csum_partial(dst, len, sum);
170}
171EXPORT_SYMBOL(csum_partial_copy_from_user);
172
173/*
174 * copy from ds while checksumming, otherwise like csum_partial
175 */
176__wsum
177csum_partial_copy(const void *src, void *dst, int len, __wsum sum)
178{
179    memcpy(dst, src, len);
180    return csum_partial(dst, len, sum);
181}
182EXPORT_SYMBOL(csum_partial_copy);
183
184#ifndef csum_tcpudp_nofold
185__wsum csum_tcpudp_nofold(__be32 saddr, __be32 daddr,
186            unsigned short len,
187            unsigned short proto,
188            __wsum sum)
189{
190    unsigned long long s = (__force u32)sum;
191
192    s += (__force u32)saddr;
193    s += (__force u32)daddr;
194#ifdef __BIG_ENDIAN
195    s += proto + len;
196#else
197    s += (proto + len) << 8;
198#endif
199    s += (s >> 32);
200    return (__force __wsum)s;
201}
202EXPORT_SYMBOL(csum_tcpudp_nofold);
203#endif
204

Archive Download this file



interactive