lib/csum.c

   1 /*
   2  * Copyright (c) 2008, 2009, 2010, 2011, 2013, 2015 Nicira, Inc.
   3  *
   4  * Licensed under the Apache License, Version 2.0 (the "License");
   5  * you may not use this file except in compliance with the License.
   6  * You may obtain a copy of the License at:
   7  *
   8  *     http://www.apache.org/licenses/LICENSE-2.0
   9  *
  10  * Unless required by applicable law or agreed to in writing, software
  11  * distributed under the License is distributed on an "AS IS" BASIS,
  12  * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
  13  * See the License for the specific language governing permissions and
  14  * limitations under the License.
  15  */
  16
  17 #include <config.h>
  18 #include "csum.h"
  19 #include "unaligned.h"
  20 #include <netinet/in.h>
  21
  22 #ifndef __CHECKER__
  23 /* Returns the IP checksum of the 'n' bytes in 'data'.
  24  *
  25  * The return value has the same endianness as the data.  That is, if 'data'
  26  * consists of a packet in network byte order, then the return value is a value
  27  * in network byte order, and if 'data' consists of a data structure in host
  28  * byte order, then the return value is in host byte order. */
  29 ovs_be16
  30 csum(const void *data, size_t n)
  31 {
  32     return csum_finish(csum_continue(0, data, n));
  33 }
  34
  35 /* Adds the 'n' bytes in 'data' to the partial IP checksum 'partial' and
  36  * returns the updated checksum.  (To start a new checksum, pass 0 for
  37  * 'partial'.  To obtain the finished checksum, pass the return value to
  38  * csum_finish().) */
  39 uint32_t
  40 csum_continue(uint32_t partial, const void *data_, size_t n)
  41 {
  42     const ovs_be16 *data = data_;
  43
  44     for (; n > 1; n -= 2, data++) {
  45         partial = csum_add16(partial, get_unaligned_be16(data));
  46     }
  47     if (n) {
  48 #ifdef WORDS_BIGENDIAN
  49         partial += (*(uint8_t *) data) << 8;
  50 #else
  51         partial += *(uint8_t *) data;
  52 #endif
  53     }
  54     return partial;
  55 }
  56
  57 /* Returns the IP checksum corresponding to 'partial', which is a value updated
  58  * by some combination of csum_add16(), csum_add32(), and csum_continue().
  59  *
  60  * The return value has the same endianness as the checksummed data.  That is,
  61  * if the data consist of a packet in network byte order, then the return value
  62  * is a value in network byte order, and if the data are a data structure in
  63  * host byte order, then the return value is in host byte order. */
  64 ovs_be16
  65 csum_finish(uint32_t partial)
  66 {
  67     while (partial >> 16) {
  68         partial = (partial & 0xffff) + (partial >> 16);
  69     }
  70     return ~partial;
  71 }
  72
  73 /* Returns the new checksum for a packet in which the checksum field previously
  74  * contained 'old_csum' and in which a field that contained 'old_u16' was
  75  * changed to contain 'new_u16'. */
  76 ovs_be16
  77 recalc_csum16(ovs_be16 old_csum, ovs_be16 old_u16, ovs_be16 new_u16)
  78 {
  79     /* Ones-complement arithmetic is endian-independent, so this code does not
  80      * use htons() or ntohs().
  81      *
  82      * See RFC 1624 for formula and explanation. */
  83     uint16_t hc_complement = ~old_csum;
  84     uint16_t m_complement = ~old_u16;
  85     uint16_t m_prime = new_u16;
  86     uint32_t sum = hc_complement + m_complement + m_prime;
  87     return csum_finish(sum);
  88 }
  89
  90 /* Returns the new checksum for a packet in which the checksum field previously
  91  * contained 'old_csum' and in which a field that contained 'old_u32' was
  92  * changed to contain 'new_u32'. */
  93 ovs_be16
  94 recalc_csum32(ovs_be16 old_csum, ovs_be32 old_u32, ovs_be32 new_u32)
  95 {
  96     return recalc_csum16(recalc_csum16(old_csum, old_u32, new_u32),
  97                          old_u32 >> 16, new_u32 >> 16);
  98 }
  99
 100 /* Returns the new checksum for a packet in which the checksum field previously
 101  * contained 'old_csum' and in which a field that contained the 6 bytes at
 102  * 'old_mac' was changed to contain the 6 bytes at 'new_mac'. */
 103 ovs_be16
 104 recalc_csum48(ovs_be16 old_csum, const struct eth_addr old_mac,
 105               const struct eth_addr new_mac)
 106 {
 107     ovs_be16 new_csum = old_csum;
 108
 109     for (int i = 0; i < 3; ++i) {
 110         new_csum = recalc_csum16(new_csum, old_mac.be16[i], new_mac.be16[i]);
 111     }
 112
 113     return new_csum;
 114 }
 115
 116 /* Returns the new checksum for a packet in which the checksum field previously
 117  * contained 'old_csum' and in which a field that contained 'old_u32[4]' was
 118  * changed to contain 'new_u32[4]'. */
 119 ovs_be16
 120 recalc_csum128(ovs_be16 old_csum, ovs_16aligned_be32 old_u32[4],
 121                const struct in6_addr *new_in6)
 122 {
 123     ovs_be16 new_csum = old_csum;
 124 #ifndef s6_addr32
 125     ovs_be32 new_u32[4];
 126     memcpy(new_u32, new_in6, sizeof new_u32);
 127 #else
 128     const ovs_be32 *new_u32 = new_in6->s6_addr32;
 129 #endif
 130     int i;
 131
 132     for (i = 0; i < 4; ++i) {
 133         new_csum = recalc_csum32(new_csum,
 134                                  get_16aligned_be32(&old_u32[i]), new_u32[i]);
 135     }
 136     return new_csum;
 137 }
 138 #else  /* __CHECKER__ */
 139 /* Making sparse happy with these functions also makes them unreadable, so
 140  * don't bother to show it their implementations. */
 141 #endif