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Diffstat (limited to 'checksum.c')
| -rw-r--r-- | checksum.c | 189 |
1 files changed, 189 insertions, 0 deletions
diff --git a/checksum.c b/checksum.c new file mode 100644 index 0000000..e6e84a2 --- /dev/null +++ b/checksum.c @@ -0,0 +1,189 @@ +/* + * Copyright (c) 1998-2006 The TCPDUMP project + * + * 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. + * + * miscellaneous checksumming routines + * + * Original code by Hannes Gredler (hannes@gredler.at) + */ + +#ifdef HAVE_CONFIG_H +#include <config.h> +#endif + +#include "netdissect-stdinc.h" + +#include <stdio.h> +#include <stdlib.h> +#include <string.h> +#include <assert.h> + +#include "netdissect.h" + +/* + * CRC-10 table generated using the following Python snippet: + +import sys + +crc_table = [] +for i in range(256): + accum = i << 2 + for j in range(8): + accum <<= 1 + if accum & 0x400: + accum ^= 0x633 + crc_table.append(accum) + +for i in range(len(crc_table)/8): + for j in range(8): + sys.stdout.write("0x%04x, " % crc_table[i*8+j]) + sys.stdout.write("\n") + + */ +static const uint16_t crc10_table[256] = +{ + 0x0000, 0x0233, 0x0255, 0x0066, 0x0299, 0x00aa, 0x00cc, 0x02ff, + 0x0301, 0x0132, 0x0154, 0x0367, 0x0198, 0x03ab, 0x03cd, 0x01fe, + 0x0031, 0x0202, 0x0264, 0x0057, 0x02a8, 0x009b, 0x00fd, 0x02ce, + 0x0330, 0x0103, 0x0165, 0x0356, 0x01a9, 0x039a, 0x03fc, 0x01cf, + 0x0062, 0x0251, 0x0237, 0x0004, 0x02fb, 0x00c8, 0x00ae, 0x029d, + 0x0363, 0x0150, 0x0136, 0x0305, 0x01fa, 0x03c9, 0x03af, 0x019c, + 0x0053, 0x0260, 0x0206, 0x0035, 0x02ca, 0x00f9, 0x009f, 0x02ac, + 0x0352, 0x0161, 0x0107, 0x0334, 0x01cb, 0x03f8, 0x039e, 0x01ad, + 0x00c4, 0x02f7, 0x0291, 0x00a2, 0x025d, 0x006e, 0x0008, 0x023b, + 0x03c5, 0x01f6, 0x0190, 0x03a3, 0x015c, 0x036f, 0x0309, 0x013a, + 0x00f5, 0x02c6, 0x02a0, 0x0093, 0x026c, 0x005f, 0x0039, 0x020a, + 0x03f4, 0x01c7, 0x01a1, 0x0392, 0x016d, 0x035e, 0x0338, 0x010b, + 0x00a6, 0x0295, 0x02f3, 0x00c0, 0x023f, 0x000c, 0x006a, 0x0259, + 0x03a7, 0x0194, 0x01f2, 0x03c1, 0x013e, 0x030d, 0x036b, 0x0158, + 0x0097, 0x02a4, 0x02c2, 0x00f1, 0x020e, 0x003d, 0x005b, 0x0268, + 0x0396, 0x01a5, 0x01c3, 0x03f0, 0x010f, 0x033c, 0x035a, 0x0169, + 0x0188, 0x03bb, 0x03dd, 0x01ee, 0x0311, 0x0122, 0x0144, 0x0377, + 0x0289, 0x00ba, 0x00dc, 0x02ef, 0x0010, 0x0223, 0x0245, 0x0076, + 0x01b9, 0x038a, 0x03ec, 0x01df, 0x0320, 0x0113, 0x0175, 0x0346, + 0x02b8, 0x008b, 0x00ed, 0x02de, 0x0021, 0x0212, 0x0274, 0x0047, + 0x01ea, 0x03d9, 0x03bf, 0x018c, 0x0373, 0x0140, 0x0126, 0x0315, + 0x02eb, 0x00d8, 0x00be, 0x028d, 0x0072, 0x0241, 0x0227, 0x0014, + 0x01db, 0x03e8, 0x038e, 0x01bd, 0x0342, 0x0171, 0x0117, 0x0324, + 0x02da, 0x00e9, 0x008f, 0x02bc, 0x0043, 0x0270, 0x0216, 0x0025, + 0x014c, 0x037f, 0x0319, 0x012a, 0x03d5, 0x01e6, 0x0180, 0x03b3, + 0x024d, 0x007e, 0x0018, 0x022b, 0x00d4, 0x02e7, 0x0281, 0x00b2, + 0x017d, 0x034e, 0x0328, 0x011b, 0x03e4, 0x01d7, 0x01b1, 0x0382, + 0x027c, 0x004f, 0x0029, 0x021a, 0x00e5, 0x02d6, 0x02b0, 0x0083, + 0x012e, 0x031d, 0x037b, 0x0148, 0x03b7, 0x0184, 0x01e2, 0x03d1, + 0x022f, 0x001c, 0x007a, 0x0249, 0x00b6, 0x0285, 0x02e3, 0x00d0, + 0x011f, 0x032c, 0x034a, 0x0179, 0x0386, 0x01b5, 0x01d3, 0x03e0, + 0x021e, 0x002d, 0x004b, 0x0278, 0x0087, 0x02b4, 0x02d2, 0x00e1 +}; + +static void +init_crc10_table(void) +{ +#define CRC10_POLYNOMIAL 0x633 + int i, j; + uint16_t accum; + uint16_t verify_crc10_table[256]; + + for ( i = 0; i < 256; i++ ) + { + accum = ((unsigned short) i << 2); + for ( j = 0; j < 8; j++ ) + { + if ((accum <<= 1) & 0x400) accum ^= CRC10_POLYNOMIAL; + } + verify_crc10_table[i] = accum; + } + assert(memcmp(verify_crc10_table, + crc10_table, + sizeof(verify_crc10_table)) == 0); +#undef CRC10_POLYNOMIAL +} + +uint16_t +verify_crc10_cksum(uint16_t accum, const u_char *p, int length) +{ + int i; + + for ( i = 0; i < length; i++ ) + { + accum = ((accum << 8) & 0x3ff) + ^ crc10_table[( accum >> 2) & 0xff] + ^ *p++; + } + return accum; +} + +/* precompute checksum tables */ +void +init_checksum(void) { + + init_crc10_table(); + +} + +/* + * 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. + */ +uint16_t +create_osi_cksum (const uint8_t *pptr, int checksum_offset, int length) +{ + + int x; + int y; + uint32_t mul; + uint32_t c0; + uint32_t c1; + uint16_t checksum; + int idx; + + c0 = 0; + c1 = 0; + + for (idx = 0; idx < length; idx++) { + /* + * Ignore the contents of the checksum field. + */ + if (idx == checksum_offset || + idx == checksum_offset+1) { + c1 += c0; + pptr++; + } else { + c0 = c0 + *(pptr++); + c1 += c0; + } + } + + c0 = c0 % 255; + c1 = c1 % 255; + + mul = (length - checksum_offset)*(c0); + + x = mul - c0 - c1; + y = c1 - mul - 1; + + if ( y >= 0 ) y++; + if ( x < 0 ) x--; + + x %= 255; + y %= 255; + + + if (x == 0) x = 255; + if (y == 0) y = 255; + + y &= 0x00FF; + checksum = ((x << 8) | y); + + return checksum; +} |