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
40static inline unsigned short from32to16(unsigned int x)
41{
42	/* add up 16-bit and 16-bit for 16+c bit */
43	x = (x & 0xffff) + (x >> 16);
44	/* add up carry.. */
45	x = (x & 0xffff) + (x >> 16);
46	return x;
47}
48
49static unsigned int do_csum(const unsigned char *buff, int len)
50{
51	int odd;
52	unsigned int result = 0;
53
54	if (len <= 0)
55		goto out;
56	odd = 1 & (unsigned long) buff;
57	if (odd) {
58#ifdef __LITTLE_ENDIAN
59		result += (*buff << 8);
60#else
61		result = *buff;
62#endif
63		len--;
64		buff++;
65	}
66	if (len >= 2) {
67		if (2 & (unsigned long) buff) {
68			result += *(unsigned short *) buff;
69			len -= 2;
70			buff += 2;
71		}
72		if (len >= 4) {
73			const unsigned char *end = buff + ((unsigned)len & ~3);
74			unsigned int carry = 0;
75			do {
76				unsigned int w = *(unsigned int *) buff;
77				buff += 4;
78				result += carry;
79				result += w;
80				carry = (w > result);
81			} while (buff < end);
82			result += carry;
83			result = (result & 0xffff) + (result >> 16);
84		}
85		if (len & 2) {
86			result += *(unsigned short *) buff;
87			buff += 2;
88		}
89	}
90	if (len & 1)
91#ifdef __LITTLE_ENDIAN
92		result += *buff;
93#else
94		result += (*buff << 8);
95#endif
96	result = from32to16(result);
97	if (odd)
98		result = ((result >> 8) & 0xff) | ((result & 0xff) << 8);
99out:
100	return result;
101}
102EXPORT_SYMBOL(ip_fast_csum);
103
104/*
105 * computes the checksum of a memory block at buff, length len,
106 * and adds in "sum" (32-bit)
107 *
108 * returns a 32-bit number suitable for feeding into itself
109 * or csum_tcpudp_magic
110 *
111 * this function must be called with even lengths, except
112 * for the last fragment, which may be odd
113 *
114 * it's best to have buff aligned on a 32-bit boundary
115 */
116__wsum csum_partial(const void *buff, int len, __wsum wsum)
117{
118	unsigned int sum = (__force unsigned int)wsum;
119	unsigned int result = do_csum(buff, len);
120
121	/* add in old sum, and carry.. */
122	result += sum;
123	if (sum > result)
124		result += 1;
125	return (__force __wsum)result;
126}
127
128/*
129 * this routine is used for miscellaneous IP-like checksums, mainly
130 * in icmp.c
131 */
132__sum16 ip_compute_csum(const void *buff, int len)
133{
134	return (__force __sum16)~do_csum(buff, len);
135}
136EXPORT_SYMBOL(ip_compute_csum);
137
138/*
139 * copy from fs while checksumming, otherwise like csum_partial
140 */
141__wsum
142csum_partial_copy_from_user(const void __user *src, void *dst, int len,
143						__wsum sum, int *csum_err)
144{
145	int missing;
146
147	missing = __copy_from_user(dst, src, len);
148	if (missing) {
149		memset(dst + len - missing, 0, missing);
150		*csum_err = -EFAULT;
151	} else
152		*csum_err = 0;
153
154	return csum_partial(dst, len, sum);
155}
156EXPORT_SYMBOL(csum_partial_copy_from_user);
157
158/*
159 * copy from ds while checksumming, otherwise like csum_partial
160 */
161__wsum
162csum_partial_copy(const void *src, void *dst, int len, __wsum sum)
163{
164	memcpy(dst, src, len);
165	return csum_partial(dst, len, sum);
166}
167EXPORT_SYMBOL(csum_partial_copy);
168