129 lines
3.8 KiB
C
129 lines
3.8 KiB
C
/*
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* Copyright (c) 1998-2006 The TCPDUMP project
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* 2014 Sage Electronic Engineering, LLC
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* All Rights Reserved
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*
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* Redistribution and use in source and binary forms, with or without
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* modification, are permitted provided that: (1) source code
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* distributions retain the above copyright notice and this paragraph
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* in its entirety, and (2) distributions including binary code include
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* the above copyright notice and this paragraph in its entirety in
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* the documentation or other materials provided with the distribution.
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* THIS SOFTWARE IS PROVIDED ``AS IS'' AND
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* WITHOUT ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, WITHOUT
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* LIMITATION, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS
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* FOR A PARTICULAR PURPOSE.
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*
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* Original code by Hannes Gredler <hannes@juniper.net>
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* Rewritten for Fletcher32 by Bruce Griffith <Bruce.Griffith@se-eng.com>
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*/
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#include <errno.h>
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#include <stdio.h>
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#include <sys/stat.h>
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#include <sys/types.h>
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#include <unistd.h>
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#include <string.h>
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#define MAX_PSP_DIRECTORY_SIZE 512
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typedef unsigned int uint32_t;
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typedef unsigned char uint8_t;
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typedef unsigned short uint16_t;
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/*
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* Creates the OSI Fletcher checksum. See 8473-1, Appendix C, section C.3.
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* The checksum field of the passed PDU does not need to be reset to zero.
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*
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* The "Fletcher Checksum" was proposed in a paper by John G. Fletcher of
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* Lawrence Livermore Labs. The Fletcher Checksum was proposed as an
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* alternative to cyclical redundancy checks because it provides error-
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* detection properties similar to cyclical redundancy checks but at the
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* cost of a simple summation technique. Its characteristics were first
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* published in IEEE Transactions on Communications in January 1982. One
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* version has been adopted by ISO for use in the class-4 transport layer
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* of the network protocol.
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*
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* This program expects:
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* stdin: The input file to compute a checksum for. The input file
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* not be longer than 256 bytes.
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* stdout: Copied from the input file with the Fletcher's Checksum
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* inserted 8 bytes after the beginning of the file.
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* stderr: Used to print out error messages.
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*/
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uint32_t fletcher32 (const uint16_t *pptr, int length)
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{
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uint32_t c0;
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uint32_t c1;
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uint32_t checksum;
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int index;
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c0 = 0xFFFF;
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c1 = 0xFFFF;
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for (index = 0; index < length; index++) {
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/*
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* Ignore the contents of the checksum field.
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*/
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c0 += *(pptr++);
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c1 += c0;
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if ((index % 360) == 0) {
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c0 = (c0 & 0xFFFF) + (c0 >> 16); // Sum0 modulo 65535 + the overflow
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c1 = (c1 & 0xFFFF) + (c1 >> 16); // Sum1 modulo 65535 + the overflow
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}
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}
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c0 = (c0 & 0xFFFF) + (c0 >> 16); // Sum0 modulo 65535 + the overflow
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c1 = (c1 & 0xFFFF) + (c1 >> 16); // Sum1 modulo 65535 + the overflow
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checksum = (c1 << 16) | c0;
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return checksum;
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}
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int main(int argc, char **argv)
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{
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uint32_t checksum = 0xFFFFFFFF;
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struct stat filestat = {};
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int retcode = EINVAL;
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size_t filesize = 0;
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char debugoption[] = "--print";
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uint16_t buffer[MAX_PSP_DIRECTORY_SIZE / sizeof(uint16_t)];
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retcode = fstat(fileno(stdin), &filestat);
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filesize = filestat.st_size;
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if (retcode < 0) {
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perror("FLETCHER32");
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return errno;
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} else if (!((12 < filesize) && (filesize <= sizeof(buffer)))) {
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fprintf(stderr, "FLETCHER32: input file is not valid for this program.\n");
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return EINVAL;
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}
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retcode = read(fileno(stdin), (void *)buffer, filesize);
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if (retcode < 0) {
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perror("FLETCHER32");
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return errno;
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}
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checksum = fletcher32(&buffer[2], filesize/2 - 2);
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*((uint32_t *)& buffer[2]) = checksum;
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#ifndef DEBUG
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if ((argc == 2) && !strncmp(argv[1], debugoption, sizeof(debugoption+1))) {
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#endif
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fprintf(stderr, "Fletcher's Checksum: %x\n", checksum);
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#ifndef DEBUG
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}
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#endif
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retcode = write(fileno(stdout), buffer, filesize);
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if (retcode < 0) {
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perror("FLETCHER32");
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return errno;
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}
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return 0;
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}
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