sys/netinet/in_cksum.c

   1 /*
   2  * Copyright (c) 2003,2004 The DragonFly Project.  All rights reserved.
   3  *
   4  * This code is derived from software contributed to The DragonFly Project
   5  * by Matthew Dillon <dillon@backplane.com>
   6  *
   7  * Redistribution and use in source and binary forms, with or without
   8  * modification, are permitted provided that the following conditions
   9  * are met:
  10  *
  11  * 1. Redistributions of source code must retain the above copyright
  12  *    notice, this list of conditions and the following disclaimer.
  13  * 2. Redistributions in binary form must reproduce the above copyright
  14  *    notice, this list of conditions and the following disclaimer in
  15  *    the documentation and/or other materials provided with the
  16  *    distribution.
  17  * 3. Neither the name of The DragonFly Project nor the names of its
  18  *    contributors may be used to endorse or promote products derived
  19  *    from this software without specific, prior written permission.
  20  *
  21  * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
  22  * ``AS IS'' AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
  23  * LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS
  24  * FOR A PARTICULAR PURPOSE ARE DISCLAIMED.  IN NO EVENT SHALL THE
  25  * COPYRIGHT HOLDERS OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT,
  26  * INCIDENTAL, SPECIAL, EXEMPLARY OR CONSEQUENTIAL DAMAGES (INCLUDING,
  27  * BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES;
  28  * LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED
  29  * AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY,
  30  * OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT
  31  * OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
  32  * SUCH DAMAGE.
  33  */
  34
  35 #include <sys/param.h>
  36 #include <sys/systm.h>
  37 #include <sys/mbuf.h>
  38 #include <sys/in_cksum.h>
  39
  40 #include <netinet/in.h>
  41 #include <netinet/in_systm.h>
  42 #include <netinet/ip.h>
  43 #include <netinet/ip_var.h>
  44
  45 #include <machine/endian.h>
  46
  47 /*
  48  * Return the 16 bit 1's complement checksum in network byte order.  Devolve
  49  * the mbuf into 32 bit aligned segments that we can pass to assembly and
  50  * do the rest manually.  Even though we return a 16 bit unsigned value,
  51  * we declare it as a 32 bit unsigned value to reduce unnecessary assembly
  52  * conversions.
  53  *
  54  * Byte ordering issues.  Note two things.  First, no secondary carry occurs,
  55  * and second, a one's complement checksum is endian-independant.  If we are
  56  * given a data buffer in network byte order, our checksum will be in network
  57  * byte order.
  58  *
  59  * 0xffff + 0xffff = 0xfffe + C = 0xffff (so no second carry occurs).
  60  *
  61  * 0x8142 + 0x8243 = 0x0385 + C = 0x0386 (checksum is in same byte order
  62  * 0x4281 + 0x4382              = 0x8603  as the data regardless of arch)
  63  *
  64  * This works with 16, 32, 64, etc... bits as long as we deal with the
  65  * carry when collapsing it back down to 16 bits.
  66  */
  67
  68 uint32_t
  69 in_cksum_range(const struct mbuf *m, int nxt, int offset, int bytes)
  70 {
  71     const uint8_t *ptr;
  72     uint32_t sum0;
  73     uint32_t sum1;
  74     int n;
  75     int flip;
  76
  77     sum0 = 0;
  78     sum1 = 0;
  79     flip = 0;
  80
  81     if (nxt != 0) {
  82         uint32_t sum32;
  83         struct ipovly ipov;
  84
  85         /* pseudo header */
  86         if (offset < sizeof(struct ipovly))
  87                 panic("in_cksum_range: offset too short");
  88         if (m->m_len < sizeof(struct ip))
  89                 panic("in_cksum_range: bad mbuf chain");
  90         bzero(&ipov, sizeof ipov);
  91         ipov.ih_len = htons(bytes);
  92         ipov.ih_pr = nxt;
  93         ipov.ih_src = mtod(m, const struct ip *)->ip_src;
  94         ipov.ih_dst = mtod(m, const struct ip *)->ip_dst;
  95         ptr = (const uint8_t *)&ipov;
  96
  97         sum32 = asm_ones32(ptr, sizeof(ipov) / 4);
  98         sum32 = (sum32 >> 16) + (sum32 & 0xffff);
  99         if (flip)
 100             sum1 += sum32;
 101         else
 102             sum0 += sum32;
 103     }
 104
 105     /*
 106      * Skip fully engulfed mbufs.  Branch predict optimal.
 107      */
 108     while (m && offset >= m->m_len) {
 109         offset -= m->m_len;
 110         m = m->m_next;
 111     }
 112
 113     /*
 114      * Process the checksum for each segment.  Note that the code below is
 115      * branch-predict optimal, so it's faster then you might otherwise
 116      * believe.  When we are buffer-aligned but also odd-byte-aligned from
 117      * the point of view of the IP packet, we accumulate to sum1 instead of
 118      * sum0.
 119      *
 120      * Initial offsets do not pre-set flip (assert that offset is even?)
 121      */
 122     while (bytes > 0 && m) {
 123         /*
 124          * Calculate pointer base and number of bytes to snarf, account
 125          * for snarfed bytes.
 126          */
 127         ptr = mtod(m, const uint8_t *) + offset;
 128         if ((n = m->m_len - offset) > bytes)
 129             n = bytes;
 130         bytes -= n;
 131
 132         /*
 133          * First 16-bit-align our buffer by eating a byte if necessary,
 134          * then 32-bit-align our buffer by eating a word if necessary.
 135          *
 136          * We are endian-sensitive when chomping a byte.  WARNING!  Be
 137          * careful optimizing this!  16 ane 32 bit words must be aligned
 138          * for this to be generic code.
 139          */
 140         if (((intptr_t)ptr & 1) && n) {
 141 #if BYTE_ORDER == LITTLE_ENDIAN
 142             if (flip)
 143                 sum1 += ptr[0];
 144             else
 145                 sum0 += ptr[0];
 146 #else
 147             if (flip)
 148                 sum0 += ptr[0];
 149             else
 150                 sum1 += ptr[0];
 151 #endif
 152             ++ptr;
 153             --n;
 154             flip = 1 - flip;
 155         }
 156         if (((intptr_t)ptr & 2) && n > 1) {
 157             if (flip)
 158                 sum1 += *(const uint16_t *)ptr;
 159             else
 160                 sum0 += *(const uint16_t *)ptr;
 161             ptr += 2;
 162             n -= 2;
 163         }
 164
 165         /*
 166          * Process a 32-bit aligned data buffer and accumulate the result
 167          * in sum0 or sum1.  Allow only one 16 bit overflow carry.
 168          */
 169         if (n >= 4) {
 170             uint32_t sum32;
 171
 172             sum32 = asm_ones32((const void *)ptr, n >> 2);
 173             sum32 = (sum32 >> 16) + (sum32 & 0xffff);
 174             if (flip)
 175                 sum1 += sum32;
 176             else
 177                 sum0 += sum32;
 178             ptr += n & ~3;
 179             /* n &= 3; dontcare */
 180         }
 181
 182         /*
 183          * Handle oddly-sized buffers.  Handle word issues first while
 184          * ptr is still aligned.
 185          */
 186         if (n & 2) {
 187             if (flip)
 188                 sum1 += *(const uint16_t *)ptr;
 189             else
 190                 sum0 += *(const uint16_t *)ptr;
 191             ptr += 2;
 192             /* n -= 2; dontcare */
 193         }
 194         if (n & 1) {
 195 #if BYTE_ORDER == LITTLE_ENDIAN
 196             if (flip)
 197                 sum1 += ptr[0];
 198             else
 199                 sum0 += ptr[0];
 200 #else
 201             if (flip)
 202                 sum0 += ptr[0];
 203             else
 204                 sum1 += ptr[0];
 205 #endif
 206             /* ++ptr; dontcare */
 207             /* --n; dontcare */
 208             flip = 1 - flip;
 209         }
 210         m = m->m_next;
 211         offset = 0;
 212     }
 213
 214     /*
 215      * Due to byte aligned or oddly-sized buffers we may have a checksum
 216      * in sum1 which needs to be shifted and added to our main sum.  There
 217      * is a presumption here that no more then 255 overflows occured which
 218      * is 255/3 byte aligned mbufs in the worst case.
 219      */
 220     sum0 += sum1 << 8;
 221     sum0 = (sum0 >> 16) + (sum0 & 0xffff);
 222     if (sum0 > 0xffff)
 223         ++sum0;
 224     return(~sum0 & 0xffff);
 225 }
 226