/* in_cksum.c | |

* 4.4-Lite-2 Internet checksum routine, modified to take a vector of | |

* pointers/lengths giving the pieces to be checksummed. Also using | |

* Tahoe/CGI version of ADDCARRY(x) macro instead of from portable version. | |

*/ | |

/* | |

* Copyright (c) 1988, 1992, 1993 | |

* The Regents of the University of California. All rights reserved. | |

* | |

* Redistribution and use in source and binary forms, with or without | |

* modification, are permitted provided that the following conditions | |

* are met: | |

* 1. Redistributions of source code must retain the above copyright | |

* notice, this list of conditions and the following disclaimer. | |

* 2. Redistributions in binary form must reproduce the above copyright | |

* notice, this list of conditions and the following disclaimer in the | |

* documentation and/or other materials provided with the distribution. | |

* 3. Neither the name of the University nor the names of its contributors | |

* may be used to endorse or promote products derived from this software | |

* without specific prior written permission. | |

* | |

* THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND | |

* ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE | |

* IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE | |

* ARE DISCLAIMED. IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE | |

* FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL | |

* DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS | |

* OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) | |

* HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT | |

* LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY | |

* OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF | |

* SUCH DAMAGE. | |

* | |

* @(#)in_cksum.c 8.1 (Berkeley) 6/10/93 | |

*/ | |

#ifdef HAVE_CONFIG_H | |

# include "config.h" | |

#endif | |

#include <netdissect-stdinc.h> | |

#include "netdissect.h" | |

/* | |

* Checksum routine for Internet Protocol family headers (Portable Version). | |

* | |

* This routine is very heavily used in the network | |

* code and should be modified for each CPU to be as fast as possible. | |

*/ | |

#define ADDCARRY(x) {if ((x) > 65535) (x) -= 65535;} | |

#define REDUCE {l_util.l = sum; sum = l_util.s[0] + l_util.s[1]; ADDCARRY(sum);} | |

uint16_t | |

in_cksum(const struct cksum_vec *vec, int veclen) | |

{ | |

register const uint16_t *w; | |

register int sum = 0; | |

register int mlen = 0; | |

int byte_swapped = 0; | |

union { | |

uint8_t c[2]; | |

uint16_t s; | |

} s_util; | |

union { | |

uint16_t s[2]; | |

uint32_t l; | |

} l_util; | |

for (; veclen != 0; vec++, veclen--) { | |

if (vec->len == 0) | |

continue; | |

w = (const uint16_t *)(const void *)vec->ptr; | |

if (mlen == -1) { | |

/* | |

* The first byte of this chunk is the continuation | |

* of a word spanning between this chunk and the | |

* last chunk. | |

* | |

* s_util.c[0] is already saved when scanning previous | |

* chunk. | |

*/ | |

s_util.c[1] = *(const uint8_t *)w; | |

sum += s_util.s; | |

w = (const uint16_t *)(const void *)((const uint8_t *)w + 1); | |

mlen = vec->len - 1; | |

} else | |

mlen = vec->len; | |

/* | |

* Force to even boundary. | |

*/ | |

if ((1 & (uintptr_t) w) && (mlen > 0)) { | |

REDUCE; | |

sum <<= 8; | |

s_util.c[0] = *(const uint8_t *)w; | |

w = (const uint16_t *)(const void *)((const uint8_t *)w + 1); | |

mlen--; | |

byte_swapped = 1; | |

} | |

/* | |

* Unroll the loop to make overhead from | |

* branches &c small. | |

*/ | |

while ((mlen -= 32) >= 0) { | |

sum += w[0]; sum += w[1]; sum += w[2]; sum += w[3]; | |

sum += w[4]; sum += w[5]; sum += w[6]; sum += w[7]; | |

sum += w[8]; sum += w[9]; sum += w[10]; sum += w[11]; | |

sum += w[12]; sum += w[13]; sum += w[14]; sum += w[15]; | |

w += 16; | |

} | |

mlen += 32; | |

while ((mlen -= 8) >= 0) { | |

sum += w[0]; sum += w[1]; sum += w[2]; sum += w[3]; | |

w += 4; | |

} | |

mlen += 8; | |

if (mlen == 0 && byte_swapped == 0) | |

continue; | |

REDUCE; | |

while ((mlen -= 2) >= 0) { | |

sum += *w++; | |

} | |

if (byte_swapped) { | |

REDUCE; | |

sum <<= 8; | |

byte_swapped = 0; | |

if (mlen == -1) { | |

s_util.c[1] = *(const uint8_t *)w; | |

sum += s_util.s; | |

mlen = 0; | |

} else | |

mlen = -1; | |

} else if (mlen == -1) | |

s_util.c[0] = *(const uint8_t *)w; | |

} | |

if (mlen == -1) { | |

/* The last mbuf has odd # of bytes. Follow the | |

standard (the odd byte may be shifted left by 8 bits | |

or not as determined by endian-ness of the machine) */ | |

s_util.c[1] = 0; | |

sum += s_util.s; | |

} | |

REDUCE; | |

return (~sum & 0xffff); | |

} | |

/* | |

* Given the host-byte-order value of the checksum field in a packet | |

* header, and the network-byte-order computed checksum of the data | |

* that the checksum covers (including the checksum itself), compute | |

* what the checksum field *should* have been. | |

*/ | |

uint16_t | |

in_cksum_shouldbe(uint16_t sum, uint16_t computed_sum) | |

{ | |

uint32_t shouldbe; | |

/* | |

* The value that should have gone into the checksum field | |

* is the negative of the value gotten by summing up everything | |

* *but* the checksum field. | |

* | |

* We can compute that by subtracting the value of the checksum | |

* field from the sum of all the data in the packet, and then | |

* computing the negative of that value. | |

* | |

* "sum" is the value of the checksum field, and "computed_sum" | |

* is the negative of the sum of all the data in the packets, | |

* so that's -(-computed_sum - sum), or (sum + computed_sum). | |

* | |

* All the arithmetic in question is one's complement, so the | |

* addition must include an end-around carry; we do this by | |

* doing the arithmetic in 32 bits (with no sign-extension), | |

* and then adding the upper 16 bits of the sum, which contain | |

* the carry, to the lower 16 bits of the sum, and then do it | |

* again in case *that* sum produced a carry. | |

* | |

* As RFC 1071 notes, the checksum can be computed without | |

* byte-swapping the 16-bit words; summing 16-bit words | |

* on a big-endian machine gives a big-endian checksum, which | |

* can be directly stuffed into the big-endian checksum fields | |

* in protocol headers, and summing words on a little-endian | |

* machine gives a little-endian checksum, which must be | |

* byte-swapped before being stuffed into a big-endian checksum | |

* field. | |

* | |

* "computed_sum" is a network-byte-order value, so we must put | |

* it in host byte order before subtracting it from the | |

* host-byte-order value from the header; the adjusted checksum | |

* will be in host byte order, which is what we'll return. | |

*/ | |

shouldbe = sum; | |

shouldbe += ntohs(computed_sum); | |

shouldbe = (shouldbe & 0xFFFF) + (shouldbe >> 16); | |

shouldbe = (shouldbe & 0xFFFF) + (shouldbe >> 16); | |

return shouldbe; | |

} |