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Linux/lib/checksum.c

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  1 // SPDX-License-Identifier: GPL-2.0-or-later
  2 /*
  3  *
  4  * INET         An implementation of the TCP/IP protocol suite for the LINUX
  5  *              operating system.  INET is implemented using the  BSD Socket
  6  *              interface as the means of communication with the user level.
  7  *
  8  *              IP/TCP/UDP checksumming routines
  9  *
 10  * Authors:     Jorge Cwik, <jorge@laser.satlink.net>
 11  *              Arnt Gulbrandsen, <agulbra@nvg.unit.no>
 12  *              Tom May, <ftom@netcom.com>
 13  *              Andreas Schwab, <schwab@issan.informatik.uni-dortmund.de>
 14  *              Lots of code moved from tcp.c and ip.c; see those files
 15  *              for more names.
 16  *
 17  * 03/02/96     Jes Sorensen, Andreas Schwab, Roman Hodek:
 18  *              Fixed some nasty bugs, causing some horrible crashes.
 19  *              A: At some points, the sum (%0) was used as
 20  *              length-counter instead of the length counter
 21  *              (%1). Thanks to Roman Hodek for pointing this out.
 22  *              B: GCC seems to mess up if one uses too many
 23  *              data-registers to hold input values and one tries to
 24  *              specify d0 and d1 as scratch registers. Letting gcc
 25  *              choose these registers itself solves the problem.
 26  */
 27 
 28 /* Revised by Kenneth Albanowski for m68knommu. Basic problem: unaligned access
 29  kills, so most of the assembly has to go. */
 30 
 31 #include <linux/export.h>
 32 #include <net/checksum.h>
 33 
 34 #include <asm/byteorder.h>
 35 
 36 #ifndef do_csum
 37 static inline unsigned short from32to16(unsigned int 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 
 46 static unsigned int do_csum(const unsigned char *buff, int len)
 47 {
 48         int odd;
 49         unsigned int result = 0;
 50 
 51         if (len <= 0)
 52                 goto out;
 53         odd = 1 & (unsigned long) buff;
 54         if (odd) {
 55 #ifdef __LITTLE_ENDIAN
 56                 result += (*buff << 8);
 57 #else
 58                 result = *buff;
 59 #endif
 60                 len--;
 61                 buff++;
 62         }
 63         if (len >= 2) {
 64                 if (2 & (unsigned long) buff) {
 65                         result += *(unsigned short *) buff;
 66                         len -= 2;
 67                         buff += 2;
 68                 }
 69                 if (len >= 4) {
 70                         const unsigned char *end = buff + ((unsigned)len & ~3);
 71                         unsigned int carry = 0;
 72                         do {
 73                                 unsigned int w = *(unsigned int *) buff;
 74                                 buff += 4;
 75                                 result += carry;
 76                                 result += w;
 77                                 carry = (w > result);
 78                         } while (buff < end);
 79                         result += carry;
 80                         result = (result & 0xffff) + (result >> 16);
 81                 }
 82                 if (len & 2) {
 83                         result += *(unsigned short *) buff;
 84                         buff += 2;
 85                 }
 86         }
 87         if (len & 1)
 88 #ifdef __LITTLE_ENDIAN
 89                 result += *buff;
 90 #else
 91                 result += (*buff << 8);
 92 #endif
 93         result = from32to16(result);
 94         if (odd)
 95                 result = ((result >> 8) & 0xff) | ((result & 0xff) << 8);
 96 out:
 97         return result;
 98 }
 99 #endif
100 
101 #ifndef ip_fast_csum
102 /*
103  *      This is a version of ip_compute_csum() optimized for IP headers,
104  *      which always checksum on 4 octet boundaries.
105  */
106 __sum16 ip_fast_csum(const void *iph, unsigned int ihl)
107 {
108         return (__force __sum16)~do_csum(iph, ihl*4);
109 }
110 EXPORT_SYMBOL(ip_fast_csum);
111 #endif
112 
113 /*
114  * computes the checksum of a memory block at buff, length len,
115  * and adds in "sum" (32-bit)
116  *
117  * returns a 32-bit number suitable for feeding into itself
118  * or csum_tcpudp_magic
119  *
120  * this function must be called with even lengths, except
121  * for the last fragment, which may be odd
122  *
123  * it's best to have buff aligned on a 32-bit boundary
124  */
125 __wsum csum_partial(const void *buff, int len, __wsum wsum)
126 {
127         unsigned int sum = (__force unsigned int)wsum;
128         unsigned int result = do_csum(buff, len);
129 
130         /* add in old sum, and carry.. */
131         result += sum;
132         if (sum > result)
133                 result += 1;
134         return (__force __wsum)result;
135 }
136 EXPORT_SYMBOL(csum_partial);
137 
138 /*
139  * this routine is used for miscellaneous IP-like checksums, mainly
140  * in icmp.c
141  */
142 __sum16 ip_compute_csum(const void *buff, int len)
143 {
144         return (__force __sum16)~do_csum(buff, len);
145 }
146 EXPORT_SYMBOL(ip_compute_csum);
147 
148 /*
149  * copy from ds while checksumming, otherwise like csum_partial
150  */
151 __wsum
152 csum_partial_copy_nocheck(const void *src, void *dst, int len, __wsum sum)
153 {
154         memcpy(dst, src, len);
155         return csum_partial(dst, len, sum);
156 }
157 EXPORT_SYMBOL(csum_partial_copy_nocheck);
158 
159 #ifndef csum_tcpudp_nofold
160 static inline u32 from64to32(u64 x)
161 {
162         /* add up 32-bit and 32-bit for 32+c bit */
163         x = (x & 0xffffffff) + (x >> 32);
164         /* add up carry.. */
165         x = (x & 0xffffffff) + (x >> 32);
166         return (u32)x;
167 }
168 
169 __wsum csum_tcpudp_nofold(__be32 saddr, __be32 daddr,
170                           __u32 len, __u8 proto, __wsum sum)
171 {
172         unsigned long long s = (__force u32)sum;
173 
174         s += (__force u32)saddr;
175         s += (__force u32)daddr;
176 #ifdef __BIG_ENDIAN
177         s += proto + len;
178 #else
179         s += (proto + len) << 8;
180 #endif
181         return (__force __wsum)from64to32(s);
182 }
183 EXPORT_SYMBOL(csum_tcpudp_nofold);
184 #endif
185 

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