Wireshark · Ethereal-dev: [Ethereal-dev] crc16

[Richard van der Hoff <richardv@xxxxxxxxxxxxx>]

As the last in my miniseries of submissions for tonight, I present a 
function to calculate a 16-bit crc, with tables for the CRC used by the 
CCITT/ITU.

It might be useful to somebody...

--
Richard van der Hoff <richardv@xxxxxxxxxxxxx>
Systems Analyst
Tel: +44 (0) 845 666 7778
http://www.mxtelecom.com

Index: crc16.c
===================================================================
RCS file: crc16.c
diff -N crc16.c
--- /dev/null	1 Jan 1970 00:00:00 -0000
+++ crc16.c	24 Jun 2004 22:24:11 -0000	1.2
@@ -0,0 +1,152 @@
+/* crc16.c
+ * CRC-16 routine
+ * 
+ * 2004 Richard van der Hoff <richardv@xxxxxxxxxxxxx>
+ *
+ * $Id: crc16.c,v 1.2 2004/06/24 22:24:11 richardv Exp $
+ *
+ * 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 "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@xxxxxxxxxxxxxxxxxxxxx.). This document is likely to be  */
+/* in the FTP archive "ftp.adelaide.edu.au/pub/rocksoft".        */
+/*                                                               */
+/*****************************************************************/
+
+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 unsigned char *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 unsigned char *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;
+}
+
+
+guint16 crc16_ccitt(const unsigned char *buf, guint len)
+{
+    return crc16_reflected(buf,len,crc16_ccitt_start,crc16_ccitt_table)
+	^ crc16_ccitt_xorout;
+}
+
+guint16 crc16_ccitt_tvb(tvbuff_t *tvb, unsigned int len)
+{
+  const unsigned char* buf = tvb_get_ptr(tvb, 0, len);
+
+  return crc16_ccitt(buf, len);
+}
Index: crc16.h
===================================================================
RCS file: crc16.h
diff -N crc16.h
--- /dev/null	1 Jan 1970 00:00:00 -0000
+++ crc16.h	24 Jun 2004 22:24:11 -0000	1.2
@@ -0,0 +1,39 @@
+/* crc16.h
+ * Declaration of CRC-16 routines and table
+ *
+ * 2004 Richard van der Hoff <richardv@xxxxxxxxxxxxx>
+ *
+ * $Id: crc16.h,v 1.2 2004/06/24 22:24:11 richardv Exp $
+ *
+ * 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.
+*/
+
+/* Calculate the CCITT/ITU/CRC-16 16-bit CRC
+   
+   (parameters for this CRC are:
+       Polynomial: x^16 + x^12 + x^5 + 1  (0x1021);
+       Start value 0xFFFF;
+       XOR result with 0xFFFF;
+       First bit is LSB)
+*/
+extern guint16 crc16_ccitt(const unsigned char *buf, guint len);
+extern guint16 crc16_ccitt_tvb(tvbuff_t *tvb, unsigned int len);
+