File: /usr/src/linux/arch/parisc/lib/checksum.c
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 * MIPS specific IP/TCP/UDP checksumming routines
7 *
8 * Authors: Ralf Baechle, <ralf@waldorf-gmbh.de>
9 * Lots of code moved from tcp.c and ip.c; see those files
10 * for more names.
11 *
12 * This program is free software; you can redistribute it and/or
13 * modify it under the terms of the GNU General Public License
14 * as published by the Free Software Foundation; either version
15 * 2 of the License, or (at your option) any later version.
16 *
17 * $Id: checksum.c,v 1.3 1997/12/01 17:57:34 ralf Exp $
18 */
19 #include <net/checksum.h>
20 #include <linux/types.h>
21 #include <asm/byteorder.h>
22 #include <asm/string.h>
23 #include <asm/uaccess.h>
24
25 static inline unsigned short from32to16(unsigned int x)
26 {
27 /* 32 bits --> 16 bits + carry */
28 x = (x & 0xffff) + (x >> 16);
29 /* 16 bits + carry --> 16 bits including carry */
30 x = (x & 0xffff) + (x >> 16);
31 return (unsigned short)x;
32 }
33
34 static inline unsigned int do_csum(const unsigned char * buff, int len)
35 {
36 int odd, count;
37 unsigned int result = 0;
38
39 if (len <= 0)
40 goto out;
41 odd = 1 & (unsigned long) buff;
42 if (odd) {
43 result = be16_to_cpu(*buff);
44 len--;
45 buff++;
46 }
47 count = len >> 1; /* nr of 16-bit words.. */
48 if (count) {
49 if (2 & (unsigned long) buff) {
50 result += *(unsigned short *) buff;
51 count--;
52 len -= 2;
53 buff += 2;
54 }
55 count >>= 1; /* nr of 32-bit words.. */
56 if (count) {
57 unsigned int carry = 0;
58 do {
59 unsigned int w = *(unsigned int *) buff;
60 count--;
61 buff += 4;
62 result += carry;
63 result += w;
64 carry = (w > result);
65 } while (count);
66 result += carry;
67 result = (result & 0xffff) + (result >> 16);
68 }
69 if (len & 2) {
70 result += *(unsigned short *) buff;
71 buff += 2;
72 }
73 }
74 if (len & 1)
75 result += le16_to_cpu(*buff);
76 result = from32to16(result);
77 if (odd)
78 result = ((result >> 8) & 0xff) | ((result & 0xff) << 8);
79 out:
80 return result;
81 }
82
83 /*
84 * computes a partial checksum, e.g. for TCP/UDP fragments
85 */
86 unsigned int csum_partial(const unsigned char *buff, int len, unsigned int sum)
87 {
88 unsigned int result = do_csum(buff, len);
89
90 /* add in old sum, and carry.. */
91 result += sum;
92 if(sum > result)
93 result += 1;
94 return result;
95 }
96
97 /*
98 * copy while checksumming, otherwise like csum_partial
99 */
100 unsigned int csum_partial_copy(const char *src, char *dst,
101 int len, unsigned int sum)
102 {
103 /*
104 * It's 2:30 am and I don't feel like doing it real ...
105 * This is lots slower than the real thing (tm)
106 */
107 sum = csum_partial(src, len, sum);
108 memcpy(dst, src, len);
109
110 return sum;
111 }
112
113 /*
114 * Copy from userspace and compute checksum. If we catch an exception
115 * then zero the rest of the buffer.
116 */
117 unsigned int csum_partial_copy_from_user (const char *src, char *dst,
118 int len, unsigned int sum,
119 int *err_ptr)
120 {
121 int missing;
122
123 missing = copy_from_user(dst, src, len);
124 if (missing) {
125 memset(dst + len - missing, 0, missing);
126 *err_ptr = -EFAULT;
127 }
128
129 return csum_partial(dst, len, sum);
130 }
131