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 <sys/types.h>
  21 #include <netinet/in.h>
  22
  23 #ifndef __CHECKER__
  24 /* Returns the IP checksum of the 'n' bytes in 'data'.
  25  *
  26  * The return value has the same endianness as the data.  That is, if 'data'
  27  * consists of a packet in network byte order, then the return value is a value
  28  * in network byte order, and if 'data' consists of a data structure in host
  29  * byte order, then the return value is in host byte order. */
  30 ovs_be16
  31 csum(const void *data, size_t n)
  32 {
  33     return csum_finish(csum_continue(0, data, n));
  34 }
  35
  36 /* Adds the 'n' bytes in 'data' to the partial IP checksum 'partial' and
  37  * returns the updated checksum.  (To start a new checksum, pass 0 for
  38  * 'partial'.  To obtain the finished checksum, pass the return value to
  39  * csum_finish().) */
  40 uint32_t
  41 csum_continue(uint32_t partial, const void *data_, size_t n)
  42 {
  43     const ovs_be16 *data = data_;
  44
  45     for (; n > 1; n -= 2, data++) {
  46         partial = csum_add16(partial, get_unaligned_be16(data));
  47     }
  48     if (n) {
  49 #ifdef WORDS_BIGENDIAN
  50         partial += (*(uint8_t *) data) << 8;
  51 #else
  52         partial += *(uint8_t *) data;
  53 #endif
  54     }
  55     return partial;
  56 }
  57
  58 /* Returns the IP checksum corresponding to 'partial', which is a value updated
  59  * by some combination of csum_add16(), csum_add32(), and csum_continue().
  60  *
  61  * The return value has the same endianness as the checksummed data.  That is,
  62  * if the data consist of a packet in network byte order, then the return value
  63  * is a value in network byte order, and if the data are a data structure in
  64  * host byte order, then the return value is in host byte order. */
  65 ovs_be16
  66 csum_finish(uint32_t partial)
  67 {
  68     while (partial >> 16) {
  69         partial = (partial & 0xffff) + (partial >> 16);
  70     }
  71     return ~partial;
  72 }
  73
  74 /* Returns the new checksum for a packet in which the checksum field previously
  75  * contained 'old_csum' and in which a field that contained 'old_u16' was
  76  * changed to contain 'new_u16'. */
  77 ovs_be16
  78 recalc_csum16(ovs_be16 old_csum, ovs_be16 old_u16, ovs_be16 new_u16)
  79 {
  80     /* Ones-complement arithmetic is endian-independent, so this code does not
  81      * use htons() or ntohs().
  82      *
  83      * See RFC 1624 for formula and explanation. */
  84     uint16_t hc_complement = ~old_csum;
  85     uint16_t m_complement = ~old_u16;
  86     uint16_t m_prime = new_u16;
  87     uint32_t sum = hc_complement + m_complement + m_prime;
  88     return csum_finish(sum);
  89 }
  90
  91 /* Returns the new checksum for a packet in which the checksum field previously
  92  * contained 'old_csum' and in which a field that contained 'old_u32' was
  93  * changed to contain 'new_u32'. */
  94 ovs_be16
  95 recalc_csum32(ovs_be16 old_csum, ovs_be32 old_u32, ovs_be32 new_u32)
  96 {
  97     return recalc_csum16(recalc_csum16(old_csum, old_u32, new_u32),
  98                          old_u32 >> 16, new_u32 >> 16);
  99 }
 100
 101 /* Returns the new checksum for a packet in which the checksum field previously
 102  * contained 'old_csum' and in which a field that contained the 6 bytes at
 103  * 'old_mac' was changed to contain the 6 bytes at 'new_mac'. */
 104 ovs_be16
 105 recalc_csum48(ovs_be16 old_csum, const struct eth_addr old_mac,
 106               const struct eth_addr new_mac)
 107 {
 108     ovs_be16 new_csum = old_csum;
 109
 110     for (int i = 0; i < 3; ++i) {
 111         new_csum = recalc_csum16(new_csum, old_mac.be16[i], new_mac.be16[i]);
 112     }
 113
 114     return new_csum;
 115 }
 116
 117 /* Returns the new checksum for a packet in which the checksum field previously
 118  * contained 'old_csum' and in which a field that contained 'old_u32[4]' was
 119  * changed to contain 'new_u32[4]'. */
 120 ovs_be16
 121 recalc_csum128(ovs_be16 old_csum, ovs_16aligned_be32 old_u32[4],
 122                const struct in6_addr *new_in6)
 123 {
 124     ovs_be16 new_csum = old_csum;
 125 #ifndef s6_addr32
 126     ovs_be32 new_u32[4];
 127     memcpy(new_u32, new_in6, sizeof new_u32);
 128 #else
 129     const ovs_be32 *new_u32 = new_in6->s6_addr32;
 130 #endif
 131     int i;
 132
 133     for (i = 0; i < 4; ++i) {
 134         new_csum = recalc_csum32(new_csum,
 135                                  get_16aligned_be32(&old_u32[i]), new_u32[i]);
 136     }
 137     return new_csum;
 138 }
 139 #else  /* __CHECKER__ */
 140 /* Making sparse happy with these functions also makes them unreadable, so
 141  * don't bother to show it their implementations. */
 142 #endif