diff options
Diffstat (limited to 'util/fletcher/fletcher.c')
| -rw-r--r-- | util/fletcher/fletcher.c | 128 |
1 files changed, 128 insertions, 0 deletions
diff --git a/util/fletcher/fletcher.c b/util/fletcher/fletcher.c new file mode 100644 index 0000000000..3147d50376 --- /dev/null +++ b/util/fletcher/fletcher.c @@ -0,0 +1,128 @@ +/* + * Copyright (c) 1998-2006 The TCPDUMP project + * 2014 Sage Electronic Engineering, LLC + * All Rights Reserved + * + * Redistribution and use in source and binary forms, with or without + * modification, are permitted provided that: (1) source code + * distributions retain the above copyright notice and this paragraph + * in its entirety, and (2) distributions including binary code include + * the above copyright notice and this paragraph in its entirety in + * the documentation or other materials provided with the distribution. + * THIS SOFTWARE IS PROVIDED ``AS IS'' AND + * WITHOUT ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, WITHOUT + * LIMITATION, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS + * FOR A PARTICULAR PURPOSE. + * + * Original code by Hannes Gredler <hannes@juniper.net> + * Rewritten for Fletcher32 by Bruce Griffith <Bruce.Griffith@se-eng.com> + */ + +#include <errno.h> +#include <stdio.h> +#include <sys/stat.h> +#include <sys/types.h> +#include <unistd.h> +#include <string.h> + +#define MAX_PSP_DIRECTORY_SIZE 512 + +typedef unsigned int uint32_t; +typedef unsigned char uint8_t; +typedef unsigned short uint16_t; + +/* + * Creates the OSI Fletcher checksum. See 8473-1, Appendix C, section C.3. + * The checksum field of the passed PDU does not need to be reset to zero. + * + * The "Fletcher Checksum" was proposed in a paper by John G. Fletcher of + * Lawrence Livermore Labs. The Fletcher Checksum was proposed as an + * alternative to cyclical redundancy checks because it provides error- + * detection properties similar to cyclical redundancy checks but at the + * cost of a simple summation technique. Its characteristics were first + * published in IEEE Transactions on Communications in January 1982. One + * version has been adopted by ISO for use in the class-4 transport layer + * of the network protocol. + * + * This program expects: + * stdin: The input file to compute a checksum for. The input file + * not be longer than 256 bytes. + * stdout: Copied from the input file with the Fletcher's Checksum + * inserted 8 bytes after the beginning of the file. + * stderr: Used to print out error messages. + */ + +uint32_t fletcher32 (const uint16_t *pptr, int length) +{ + + uint32_t c0; + uint32_t c1; + uint32_t checksum; + int index; + + c0 = 0xFFFF; + c1 = 0xFFFF; + + for (index = 0; index < length; index++) { + /* + * Ignore the contents of the checksum field. + */ + c0 += *(pptr++); + c1 += c0; + if ((index % 360) == 0) { + c0 = (c0 & 0xFFFF) + (c0 >> 16); // Sum0 modulo 65535 + the overflow + c1 = (c1 & 0xFFFF) + (c1 >> 16); // Sum1 modulo 65535 + the overflow + } + + } + + c0 = (c0 & 0xFFFF) + (c0 >> 16); // Sum0 modulo 65535 + the overflow + c1 = (c1 & 0xFFFF) + (c1 >> 16); // Sum1 modulo 65535 + the overflow + checksum = (c1 << 16) | c0; + + return checksum; +} + +int main(int argc, char **argv) +{ + uint32_t checksum = 0xFFFFFFFF; + struct stat filestat = {}; + int retcode = EINVAL; + size_t filesize = 0; + char debugoption[] = "--print"; + + uint16_t buffer[MAX_PSP_DIRECTORY_SIZE / sizeof(uint16_t)]; + + retcode = fstat(fileno(stdin), &filestat); + filesize = filestat.st_size; + if (retcode < 0) { + perror("FLETCHER32"); + return errno; + } else if (!((12 < filesize) && (filesize <= sizeof(buffer)))) { + fprintf(stderr, "FLETCHER32: input file is not valid for this program.\n"); + return EINVAL; + } + retcode = read(fileno(stdin), (void *)buffer, filesize); + if (retcode < 0) { + perror("FLETCHER32"); + return errno; + } + + checksum = fletcher32(&buffer[2], filesize/2 - 2); + *((uint32_t *)& buffer[2]) = checksum; +#ifndef DEBUG + if ((argc == 2) && !strncmp(argv[1], debugoption, sizeof(debugoption+1))) { +#endif + fprintf(stderr, "Fletcher's Checksum: %x\n", checksum); +#ifndef DEBUG + } +#endif + + retcode = write(fileno(stdout), buffer, filesize); + if (retcode < 0) { + perror("FLETCHER32"); + return errno; + } + + return 0; +} |