#ifndef lint static char sccsid[] = "@(#)crc.c 1.4 88/12/21"; #endif #include "cbratp.h" u_short ctab[] = { 0x0000, 0x1021, 0x2042, 0x3063, /* 0x00 - 0x03 */ 0x4084, 0x50a5, 0x60c6, 0x70e7, /* 0x04 - 0x07 */ 0x8108, 0x9129, 0xa14a, 0xb16b, /* 0x08 - 0x0b */ 0xc18c, 0xd1ad, 0xe1ce, 0xf1ef, /* 0x0c - 0x0f */ 0x1231, 0x0210, 0x3273, 0x2252, /* 0x10 - 0x13 */ 0x52b5, 0x4294, 0x72f7, 0x62d6, /* 0x14 - 0x17 */ 0x9339, 0x8318, 0xb37b, 0xa35a, /* 0x18 - 0x1b */ 0xd3bd, 0xc39c, 0xf3ff, 0xe3de, /* 0x1c - 0x1f */ 0x2462, 0x3443, 0x0420, 0x1401, /* 0x20 - 0x23 */ 0x64e6, 0x74c7, 0x44a4, 0x5485, /* 0x24 - 0x27 */ 0xa56a, 0xb54b, 0x8528, 0x9509, /* 0x28 - 0x2b */ 0xe5ee, 0xf5cf, 0xc5ac, 0xd58d, /* 0x2c - 0x2f */ 0x3653, 0x2672, 0x1611, 0x0630, /* 0x30 - 0x33 */ 0x76d7, 0x66f6, 0x5695, 0x46b4, /* 0x34 - 0x37 */ 0xb75b, 0xa77a, 0x9719, 0x8738, /* 0x38 - 0x3b */ 0xf7df, 0xe7fe, 0xd79d, 0xc7bc, /* 0x3c - 0x3f */ 0x48c4, 0x58e5, 0x6886, 0x78a7, /* 0x40 - 0x43 */ 0x0840, 0x1861, 0x2802, 0x3823, /* 0x44 - 0x47 */ 0xc9cc, 0xd9ed, 0xe98e, 0xf9af, /* 0x48 - 0x4b */ 0x8948, 0x9969, 0xa90a, 0xb92b, /* 0x4c - 0x4f */ 0x5af5, 0x4ad4, 0x7ab7, 0x6a96, /* 0x50 - 0x53 */ 0x1a71, 0x0a50, 0x3a33, 0x2a12, /* 0x54 - 0x57 */ 0xdbfd, 0xcbdc, 0xfbbf, 0xeb9e, /* 0x58 - 0x5b */ 0x9b79, 0x8b58, 0xbb3b, 0xab1a, /* 0x5c - 0x5f */ 0x6ca6, 0x7c87, 0x4ce4, 0x5cc5, /* 0x60 - 0x63 */ 0x2c22, 0x3c03, 0x0c60, 0x1c41, /* 0x64 - 0x67 */ 0xedae, 0xfd8f, 0xcdec, 0xddcd, /* 0x68 - 0x6b */ 0xad2a, 0xbd0b, 0x8d68, 0x9d49, /* 0x6c - 0x6f */ 0x7e97, 0x6eb6, 0x5ed5, 0x4ef4, /* 0x70 - 0x73 */ 0x3e13, 0x2e32, 0x1e51, 0x0e70, /* 0x74 - 0x77 */ 0xff9f, 0xefbe, 0xdfdd, 0xcffc, /* 0x78 - 0x7b */ 0xbf1b, 0xaf3a, 0x9f59, 0x8f78, /* 0x7c - 0x7f */ 0x9188, 0x81a9, 0xb1ca, 0xa1eb, /* 0x80 - 0x83 */ 0xd10c, 0xc12d, 0xf14e, 0xe16f, /* 0x84 - 0x87 */ 0x1080, 0x00a1, 0x30c2, 0x20e3, /* 0x88 - 0x8b */ 0x5004, 0x4025, 0x7046, 0x6067, /* 0x8c - 0x8f */ 0x83b9, 0x9398, 0xa3fb, 0xb3da, /* 0x90 - 0x93 */ 0xc33d, 0xd31c, 0xe37f, 0xf35e, /* 0x94 - 0x97 */ 0x02b1, 0x1290, 0x22f3, 0x32d2, /* 0x98 - 0x9b */ 0x4235, 0x5214, 0x6277, 0x7256, /* 0x9c - 0x9f */ 0xb5ea, 0xa5cb, 0x95a8, 0x8589, /* 0xa0 - 0xa3 */ 0xf56e, 0xe54f, 0xd52c, 0xc50d, /* 0xa4 - 0xa7 */ 0x34e2, 0x24c3, 0x14a0, 0x0481, /* 0xa8 - 0xab */ 0x7466, 0x6447, 0x5424, 0x4405, /* 0xac - 0xaf */ 0xa7db, 0xb7fa, 0x8799, 0x97b8, /* 0xb0 - 0xb3 */ 0xe75f, 0xf77e, 0xc71d, 0xd73c, /* 0xb4 - 0xb7 */ 0x26d3, 0x36f2, 0x0691, 0x16b0, /* 0xb8 - 0xbb */ 0x6657, 0x7676, 0x4615, 0x5634, /* 0xbc - 0xbf */ 0xd94c, 0xc96d, 0xf90e, 0xe92f, /* 0xc0 - 0xc3 */ 0x99c8, 0x89e9, 0xb98a, 0xa9ab, /* 0xc4 - 0xc7 */ 0x5844, 0x4865, 0x7806, 0x6827, /* 0xc8 - 0xcb */ 0x18c0, 0x08e1, 0x3882, 0x28a3, /* 0xcc - 0xcf */ 0xcb7d, 0xdb5c, 0xeb3f, 0xfb1e, /* 0xd0 - 0xd3 */ 0x8bf9, 0x9bd8, 0xabbb, 0xbb9a, /* 0xd4 - 0xd7 */ 0x4a75, 0x5a54, 0x6a37, 0x7a16, /* 0xd8 - 0xdb */ 0x0af1, 0x1ad0, 0x2ab3, 0x3a92, /* 0xdc - 0xdf */ 0xfd2e, 0xed0f, 0xdd6c, 0xcd4d, /* 0xe0 - 0xe3 */ 0xbdaa, 0xad8b, 0x9de8, 0x8dc9, /* 0xe4 - 0xe7 */ 0x7c26, 0x6c07, 0x5c64, 0x4c45, /* 0xe8 - 0xeb */ 0x3ca2, 0x2c83, 0x1ce0, 0x0cc1, /* 0xec - 0xef */ 0xef1f, 0xff3e, 0xcf5d, 0xdf7c, /* 0xf0 - 0xf3 */ 0xaf9b, 0xbfba, 0x8fd9, 0x9ff8, /* 0xf4 - 0xf7 */ 0x6e17, 0x7e36, 0x4e55, 0x5e74, /* 0xf8 - 0xfb */ 0x2e93, 0x3eb2, 0x0ed1, 0x1ef0 /* 0xfc - 0xff */ }; /************************************************************************ * these generate a CRC value from the len bytes of data contained * in the buflet chain at pc, starting at offset off. The CRC will be * generated using the CCITT specified polynomial: * * x**16 + x**12 + x**5 + 1 * * getcrc uses a compile-time vector table to speed calculation. The * table is based on the following theory... * * ...given an existing CRC, with bits: * * C15 C14 C13 C12 C11 C10 C9 C8 C7 C6 C5 C4 C3 C2 C1 C0 * * ...run it through the CRC algorithm with byte: * * D7 D6 D5 D4 D3 D2 D1 D0 * * ...and the following result will be produced: * * C7 C6 C5 C4 C3 C2 C1 C0 D7 D6 D5 D4 D3 D2 D1 D0 * C11 C10 C9 C15 C14 C13 C12 C11 C15 C14 C13 C12 C11 C10 C9 C8 * C15 C14 C13 C8 C15 C10 C9 C8 C15 C14 C13 C12 * C12 C14 C13 C12 * * ...where all bits in each column are exculsive ORed. Notice all the * exlusive ORs of bits are from the upper byte of the original CRC. * Thus, from that byte, we can create a table of 256 words which, when * exclusive ORed with the low byte of the original CRC shifted up to * the top and added to the input byte, will produce a resulting CRC. * * The data array at pd is assumed to contain at least len data bytes. * * Returns: getcrc returns a 16 bit CRC. Since X.25 insists a CRC is to * be transmitted hob first, the returned CRC will be reversed. * ************************************************************************/ u_short calculate_crc(pd, len) register u_char *pd; register short len; { register u_short crc; if (crc_mode) return 0; for (crc=~0; len>0; len--) crc = (crc << 8) ^ ctab[(crc >> 8) ^ *pd++]; return ~crc; } adjust_crc(crc, c) register u_short crc; u_char c; { extern u_short ctab[]; if (crc_mode) return 0; crc = ~crc; crc = (crc << 8) ^ ctab[(crc >> 8) ^ c]; return ~crc; } check_crc(control) u_char control; { register u_short crc; register u_short data_crc; struct frame *f = &in_coming[SEQ(control)]; if (SYNC&control) { if (crc_mode == 0) return 1; crc = calculate_crc(&control, 1); } else { if (crc_mode) { f->f_len = reader.ptr - f->f_buf; return 1; } f->f_len = reader.ptr - f->f_buf - 2; crc = calculate_crc(f->f_buf, f->f_len); crc = adjust_crc(crc, control); } data_crc = ((*(reader.ptr - 2)&0xff) << 8) | (*(reader.ptr - 1)&0xff); return data_crc == crc; }