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/export.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;
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);
100out:
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}
114EXPORT_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}
140EXPORT_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}
150EXPORT_SYMBOL(ip_compute_csum);
151
152/*
153 * copy from fs while checksumming, otherwise like csum_partial
154 */
155__wsum
156csum_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}
170EXPORT_SYMBOL(csum_partial_copy_from_user);
171
172/*
173 * copy from ds while checksumming, otherwise like csum_partial
174 */
175__wsum
176csum_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}
181EXPORT_SYMBOL(csum_partial_copy);
182
183#ifndef csum_tcpudp_nofold
184__wsum csum_tcpudp_nofold(__be32 saddr, __be32 daddr,
185            unsigned short len,
186            unsigned short proto,
187            __wsum sum)
188{
189    unsigned long long s = (__force u32)sum;
190
191    s += (__force u32)saddr;
192    s += (__force u32)daddr;
193#ifdef __BIG_ENDIAN
194    s += proto + len;
195#else
196    s += (proto + len) << 8;
197#endif
198    s += (s >> 32);
199    return (__force __wsum)s;
200}
201EXPORT_SYMBOL(csum_tcpudp_nofold);
202#endif
203

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