1/* 2 * ppphdlc.c 3 * 4 * Copied from C. S. Ananian's linux client ppp_fcs.c 5 * This code can also be found in RFC1662 6 * 7 * $Id: ppphdlc.c,v 1.1.1.1 2002/06/21 08:52:00 fenix_nl Exp $ 8 */ 9 10/* Fast Frame Check Sequence (FCS) Implementation, for HDLC-like framing of 11 * PPP. Adapted by C. Scott Ananian <cananian@alumni.princeton.edu> 12 * from RFC1662: 13 * 14 * C.2. 16-bit FCS Computation Method 15 * 16 * The following code provides a table lookup computation for 17 * calculating the Frame Check Sequence as data arrives at the 18 * interface. This implementation is based on [7], [8], and [9]. 19 * 20 * [7] Perez, "Byte-wise CRC Calculations", IEEE Micro, June 1983. 21 * 22 * [8] Morse, G., "Calculating CRC's by Bits and Bytes", Byte, 23 * September 1986. 24 * 25 * [9] LeVan, J., "A Fast CRC", Byte, November 1987. 26 */ 27 28#ifdef HAVE_CONFIG_H 29#include "config.h" 30#endif 31 32#include <sys/types.h> 33#include "ppphdlc.h" 34 35/* 36 * FCS lookup table as calculated by the table generator. 37 */ 38u_int16_t fcstab[256] = 39{ 40 0x0000, 0x1189, 0x2312, 0x329b, 0x4624, 0x57ad, 0x6536, 0x74bf, 41 0x8c48, 0x9dc1, 0xaf5a, 0xbed3, 0xca6c, 0xdbe5, 0xe97e, 0xf8f7, 42 0x1081, 0x0108, 0x3393, 0x221a, 0x56a5, 0x472c, 0x75b7, 0x643e, 43 0x9cc9, 0x8d40, 0xbfdb, 0xae52, 0xdaed, 0xcb64, 0xf9ff, 0xe876, 44 0x2102, 0x308b, 0x0210, 0x1399, 0x6726, 0x76af, 0x4434, 0x55bd, 45 0xad4a, 0xbcc3, 0x8e58, 0x9fd1, 0xeb6e, 0xfae7, 0xc87c, 0xd9f5, 46 0x3183, 0x200a, 0x1291, 0x0318, 0x77a7, 0x662e, 0x54b5, 0x453c, 47 0xbdcb, 0xac42, 0x9ed9, 0x8f50, 0xfbef, 0xea66, 0xd8fd, 0xc974, 48 0x4204, 0x538d, 0x6116, 0x709f, 0x0420, 0x15a9, 0x2732, 0x36bb, 49 0xce4c, 0xdfc5, 0xed5e, 0xfcd7, 0x8868, 0x99e1, 0xab7a, 0xbaf3, 50 0x5285, 0x430c, 0x7197, 0x601e, 0x14a1, 0x0528, 0x37b3, 0x263a, 51 0xdecd, 0xcf44, 0xfddf, 0xec56, 0x98e9, 0x8960, 0xbbfb, 0xaa72, 52 0x6306, 0x728f, 0x4014, 0x519d, 0x2522, 0x34ab, 0x0630, 0x17b9, 53 0xef4e, 0xfec7, 0xcc5c, 0xddd5, 0xa96a, 0xb8e3, 0x8a78, 0x9bf1, 54 0x7387, 0x620e, 0x5095, 0x411c, 0x35a3, 0x242a, 0x16b1, 0x0738, 55 0xffcf, 0xee46, 0xdcdd, 0xcd54, 0xb9eb, 0xa862, 0x9af9, 0x8b70, 56 0x8408, 0x9581, 0xa71a, 0xb693, 0xc22c, 0xd3a5, 0xe13e, 0xf0b7, 57 0x0840, 0x19c9, 0x2b52, 0x3adb, 0x4e64, 0x5fed, 0x6d76, 0x7cff, 58 0x9489, 0x8500, 0xb79b, 0xa612, 0xd2ad, 0xc324, 0xf1bf, 0xe036, 59 0x18c1, 0x0948, 0x3bd3, 0x2a5a, 0x5ee5, 0x4f6c, 0x7df7, 0x6c7e, 60 0xa50a, 0xb483, 0x8618, 0x9791, 0xe32e, 0xf2a7, 0xc03c, 0xd1b5, 61 0x2942, 0x38cb, 0x0a50, 0x1bd9, 0x6f66, 0x7eef, 0x4c74, 0x5dfd, 62 0xb58b, 0xa402, 0x9699, 0x8710, 0xf3af, 0xe226, 0xd0bd, 0xc134, 63 0x39c3, 0x284a, 0x1ad1, 0x0b58, 0x7fe7, 0x6e6e, 0x5cf5, 0x4d7c, 64 0xc60c, 0xd785, 0xe51e, 0xf497, 0x8028, 0x91a1, 0xa33a, 0xb2b3, 65 0x4a44, 0x5bcd, 0x6956, 0x78df, 0x0c60, 0x1de9, 0x2f72, 0x3efb, 66 0xd68d, 0xc704, 0xf59f, 0xe416, 0x90a9, 0x8120, 0xb3bb, 0xa232, 67 0x5ac5, 0x4b4c, 0x79d7, 0x685e, 0x1ce1, 0x0d68, 0x3ff3, 0x2e7a, 68 0xe70e, 0xf687, 0xc41c, 0xd595, 0xa12a, 0xb0a3, 0x8238, 0x93b1, 69 0x6b46, 0x7acf, 0x4854, 0x59dd, 0x2d62, 0x3ceb, 0x0e70, 0x1ff9, 70 0xf78f, 0xe606, 0xd49d, 0xc514, 0xb1ab, 0xa022, 0x92b9, 0x8330, 71 0x7bc7, 0x6a4e, 0x58d5, 0x495c, 0x3de3, 0x2c6a, 0x1ef1, 0x0f78 72}; 73 74#ifndef PPPINITFCS16 75#define PPPINITFCS16 0xffff /* Initial FCS value */ 76#endif 77#ifndef PPPGOODFCS16 78#define PPPGOODFCS16 0xf0b8 /* Good final FCS value */ 79#endif 80 81#if 0 82/* 83 * Calculate a new fcs given the current fcs and the new data. 84 * 85 * "#if 0" since the checksumming is now done 'on the fly' 86 */ 87u_int16_t pppfcs16(u_int16_t fcs, void *_cp, int len) 88{ 89 register unsigned char *cp = (unsigned char *) _cp; 90 91 while (len--) 92 fcs = (fcs >> 8) ^ fcstab[(fcs ^ *cp++) & 0xff]; 93 94 return (fcs); 95} 96#endif 97