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Diffstat (limited to 'epan/crc16.c')
| -rw-r--r-- | epan/crc16.c | 182 |
1 files changed, 182 insertions, 0 deletions
diff --git a/epan/crc16.c b/epan/crc16.c new file mode 100644 index 0000000000..a371ffe77c --- /dev/null +++ b/epan/crc16.c @@ -0,0 +1,182 @@ +/* crc16.c + * CRC-16 routine + * + * 2004 Richard van der Hoff <richardv@mxtelecom.com> + * + * $Id$ + * + * Ethereal - Network traffic analyzer + * By Gerald Combs <gerald@xxxxxxxxxxxx> + * Copyright 1998 Gerald Combs + * + * Copied from README.developer + * + * This program is free software; you can redistribute it and/or + * modify it under the terms of the GNU General Public License + * as published by the Free Software Foundation; either version 2 + * of the License, or (at your option) any later version. + * + * This program is distributed in the hope that it will be useful, + * but WITHOUT ANY WARRANTY; without even the implied warranty of + * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the + * GNU General Public License for more details. + * + * You should have received a copy of the GNU General Public License + * along with this program; if not, write to the Free Software + * Foundation, Inc., 59 Temple Place - Suite 330, Boston, MA 02111-1307, USA. + * + * References: + * "A Painless Guide to CRC Error Detection Algorithms", Ross Williams + * http://www.repairfaq.org/filipg/LINK/F_crc_v3.html + * + * ITU-T Recommendation V.42 (2002), "Error-Correcting Procedures for + * DCEs using asynchronous-to-synchronous conversion", Para. 8.1.1.6.1 + */ + +#include <glib.h> +#include <epan/tvbuff.h> +#include <epan/crc16.h> + + +/*****************************************************************/ + +/* + * Table for the CCITT/ITU/CRC-16 16-bit CRC + * + * Polynomial is + * + * x^16 + x^12 + x^5 + 1 + */ + +/* */ +/* CRC LOOKUP TABLE */ +/* ================ */ +/* The following CRC lookup table was generated automagically */ +/* by the Rocksoft^tm Model CRC Algorithm Table Generation */ +/* Program V1.0 using the following model parameters: */ +/* */ +/* Width : 2 bytes. */ +/* Poly : 0x1021 */ +/* Reverse : TRUE. */ +/* */ +/* For more information on the Rocksoft^tm Model CRC Algorithm, */ +/* see the document titled "A Painless Guide to CRC Error */ +/* Detection Algorithms" by Ross Williams */ +/* (ross@xxxxxxxxxxxxxxxxxxxxxx). This document is likely to be */ +/* in the FTP archive "ftp.adelaide.edu.au/pub/rocksoft". */ +/* */ +/*****************************************************************/ + +static const guint crc16_ccitt_table[256] = +{ + 0x0000, 0x1189, 0x2312, 0x329B, 0x4624, 0x57AD, 0x6536, 0x74BF, + 0x8C48, 0x9DC1, 0xAF5A, 0xBED3, 0xCA6C, 0xDBE5, 0xE97E, 0xF8F7, + 0x1081, 0x0108, 0x3393, 0x221A, 0x56A5, 0x472C, 0x75B7, 0x643E, + 0x9CC9, 0x8D40, 0xBFDB, 0xAE52, 0xDAED, 0xCB64, 0xF9FF, 0xE876, + 0x2102, 0x308B, 0x0210, 0x1399, 0x6726, 0x76AF, 0x4434, 0x55BD, + 0xAD4A, 0xBCC3, 0x8E58, 0x9FD1, 0xEB6E, 0xFAE7, 0xC87C, 0xD9F5, + 0x3183, 0x200A, 0x1291, 0x0318, 0x77A7, 0x662E, 0x54B5, 0x453C, + 0xBDCB, 0xAC42, 0x9ED9, 0x8F50, 0xFBEF, 0xEA66, 0xD8FD, 0xC974, + 0x4204, 0x538D, 0x6116, 0x709F, 0x0420, 0x15A9, 0x2732, 0x36BB, + 0xCE4C, 0xDFC5, 0xED5E, 0xFCD7, 0x8868, 0x99E1, 0xAB7A, 0xBAF3, + 0x5285, 0x430C, 0x7197, 0x601E, 0x14A1, 0x0528, 0x37B3, 0x263A, + 0xDECD, 0xCF44, 0xFDDF, 0xEC56, 0x98E9, 0x8960, 0xBBFB, 0xAA72, + 0x6306, 0x728F, 0x4014, 0x519D, 0x2522, 0x34AB, 0x0630, 0x17B9, + 0xEF4E, 0xFEC7, 0xCC5C, 0xDDD5, 0xA96A, 0xB8E3, 0x8A78, 0x9BF1, + 0x7387, 0x620E, 0x5095, 0x411C, 0x35A3, 0x242A, 0x16B1, 0x0738, + 0xFFCF, 0xEE46, 0xDCDD, 0xCD54, 0xB9EB, 0xA862, 0x9AF9, 0x8B70, + 0x8408, 0x9581, 0xA71A, 0xB693, 0xC22C, 0xD3A5, 0xE13E, 0xF0B7, + 0x0840, 0x19C9, 0x2B52, 0x3ADB, 0x4E64, 0x5FED, 0x6D76, 0x7CFF, + 0x9489, 0x8500, 0xB79B, 0xA612, 0xD2AD, 0xC324, 0xF1BF, 0xE036, + 0x18C1, 0x0948, 0x3BD3, 0x2A5A, 0x5EE5, 0x4F6C, 0x7DF7, 0x6C7E, + 0xA50A, 0xB483, 0x8618, 0x9791, 0xE32E, 0xF2A7, 0xC03C, 0xD1B5, + 0x2942, 0x38CB, 0x0A50, 0x1BD9, 0x6F66, 0x7EEF, 0x4C74, 0x5DFD, + 0xB58B, 0xA402, 0x9699, 0x8710, 0xF3AF, 0xE226, 0xD0BD, 0xC134, + 0x39C3, 0x284A, 0x1AD1, 0x0B58, 0x7FE7, 0x6E6E, 0x5CF5, 0x4D7C, + 0xC60C, 0xD785, 0xE51E, 0xF497, 0x8028, 0x91A1, 0xA33A, 0xB2B3, + 0x4A44, 0x5BCD, 0x6956, 0x78DF, 0x0C60, 0x1DE9, 0x2F72, 0x3EFB, + 0xD68D, 0xC704, 0xF59F, 0xE416, 0x90A9, 0x8120, 0xB3BB, 0xA232, + 0x5AC5, 0x4B4C, 0x79D7, 0x685E, 0x1CE1, 0x0D68, 0x3FF3, 0x2E7A, + 0xE70E, 0xF687, 0xC41C, 0xD595, 0xA12A, 0xB0A3, 0x8238, 0x93B1, + 0x6B46, 0x7ACF, 0x4854, 0x59DD, 0x2D62, 0x3CEB, 0x0E70, 0x1FF9, + 0xF78F, 0xE606, 0xD49D, 0xC514, 0xB1AB, 0xA022, 0x92B9, 0x8330, + 0x7BC7, 0x6A4E, 0x58D5, 0x495C, 0x3DE3, 0x2C6A, 0x1EF1, 0x0F78 +}; + +static const guint16 crc16_ccitt_start = 0xFFFF; +static const guint16 crc16_ccitt_xorout = 0xFFFF; + +/* two types of crcs are possible: unreflected (bits shift left) and + * reflected (bits shift right). + */ +#if 0 +static guint16 crc16_unreflected(const guint8 *buf, guint len, + guint16 crc_in, const guint table[]) +{ + /* we use guints, rather than guint16s, as they are likely to be + faster. We just ignore the top 16 bits and let them do what they want. */ + guint crc16 = (guint)crc_in;; + + while( len-- != 0 ) + crc16 = table[(crc16 ^ *buf++) & 0xff] ^ (crc16 << 8); + + return (guint16)crc16; +} +#endif + +static guint16 crc16_reflected(const guint8 *buf, guint len, + guint16 crc_in, const guint table[]) +{ + /* we use guints, rather than guint16s, as they are likely to be + faster. We just ignore the top 16 bits and let them do what they want. + XXX - does any time saved not zero-extending guint16's to 32 bits + into a register outweigh any increased cache footprint from the + larger CRC table? */ + guint crc16 = (guint)crc_in; + + while( len-- != 0 ) + crc16 = table[(crc16 ^ *buf++) & 0xff] ^ (crc16 >> 8); + + return (guint16)crc16; +} + +guint16 crc16_ccitt(const guint8 *buf, guint len) +{ + return crc16_reflected(buf,len,crc16_ccitt_start,crc16_ccitt_table) + ^ crc16_ccitt_xorout; +} + +guint16 crc16_ccitt_seed(const guint8 *buf, guint len, guint16 seed) +{ + return crc16_reflected(buf,len,seed,crc16_ccitt_table) + ^ crc16_ccitt_xorout; +} + +guint16 crc16_ccitt_tvb(tvbuff_t *tvb, guint len) +{ + const guint8* buf = tvb_get_ptr(tvb, 0, len); + + return crc16_ccitt(buf, len); +} + +guint16 crc16_ccitt_tvb_offset(tvbuff_t *tvb, guint offset, guint len) +{ + const guint8* buf = tvb_get_ptr(tvb, offset, len); + + return crc16_ccitt(buf, len); +} + +guint16 crc16_ccitt_tvb_seed(tvbuff_t *tvb, guint len, guint16 seed) +{ + const guint8* buf = tvb_get_ptr(tvb, 0, len); + + return crc16_ccitt_seed(buf, len, seed); +} + +guint16 crc16_ccitt_tvb_offset_seed(tvbuff_t *tvb, guint offset, guint len, guint16 seed) +{ + const guint8* buf = tvb_get_ptr(tvb, offset, len); + + return crc16_ccitt_seed(buf, len, seed); +} + |