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C/C++ Source or Header  |  1995-08-13  |  3.3 KB  |  83 lines
  1. /*
  2.         Cyclic redundancy check calculation routines
  3.  
  4.                 John Walker  --  May 1973
  5.  
  6. */
  7.  
  8. /*    This is the precomputed remainder table for generating and
  9.     checking cyclic redundancy check characters.  */
  10.  
  11. static unsigned char low8[] = {
  12.     0x00,0xC1,0x81,0x40,0x01,0xC0,0x80,0x41,0x01,0xC0,
  13.     0x80,0x41,0x00,0xC1,0x81,0x40,0x01,0xC0,0x80,0x41,
  14.     0x00,0xC1,0x81,0x40,0x00,0xC1,0x81,0x40,0x01,0xC0,
  15.     0x80,0x41,0x01,0xC0,0x80,0x41,0x00,0xC1,0x81,0x40,
  16.     0x00,0xC1,0x81,0x40,0x01,0xC0,0x80,0x41,0x00,0xC1,
  17.     0x81,0x40,0x01,0xC0,0x80,0x41,0x01,0xC0,0x80,0x41,
  18.     0x00,0xC1,0x81,0x40,0x01,0xC0,0x80,0x41,0x00,0xC1,
  19.     0x81,0x40,0x00,0xC1,0x81,0x40,0x01,0xC0,0x80,0x41,
  20.     0x00,0xC1,0x81,0x40,0x01,0xC0,0x80,0x41,0x01,0xC0,
  21.     0x80,0x41,0x00,0xC1,0x81,0x40,0x00,0xC1,0x81,0x40,
  22.     0x01,0xC0,0x80,0x41,0x01,0xC0,0x80,0x41,0x00,0xC1,
  23.     0x81,0x40,0x01,0xC0,0x80,0x41,0x00,0xC1,0x81,0x40,
  24.     0x00,0xC1,0x81,0x40,0x01,0xC0,0x80,0x41,0x01,0xC0,
  25.     0x80,0x41,0x00,0xC1,0x81,0x40,0x00,0xC1,0x81,0x40,
  26.     0x01,0xC0,0x80,0x41,0x00,0xC1,0x81,0x40,0x01,0xC0,
  27.     0x80,0x41,0x01,0xC0,0x80,0x41,0x00,0xC1,0x81,0x40,
  28.     0x00,0xC1,0x81,0x40,0x01,0xC0,0x80,0x41,0x01,0xC0,
  29.     0x80,0x41,0x00,0xC1,0x81,0x40,0x01,0xC0,0x80,0x41,
  30.     0x00,0xC1,0x81,0x40,0x00,0xC1,0x81,0x40,0x01,0xC0,
  31.     0x80,0x41,0x00,0xC1,0x81,0x40,0x01,0xC0,0x80,0x41,
  32.     0x01,0xC0,0x80,0x41,0x00,0xC1,0x81,0x40,0x01,0xC0,
  33.     0x80,0x41,0x00,0xC1,0x81,0x40,0x00,0xC1,0x81,0x40,
  34.     0x01,0xC0,0x80,0x41,0x01,0xC0,0x80,0x41,0x00,0xC1,
  35.     0x81,0x40,0x00,0xC1,0x81,0x40,0x01,0xC0,0x80,0x41,
  36.     0x00,0xC1,0x81,0x40,0x01,0xC0,0x80,0x41,0x01,0xC0,
  37.     0x80,0x41,0x00,0xC1,0x81,0x40
  38. };
  39.  
  40. static unsigned char high8[] = {
  41.     0x00,0xC0,0xC1,0x01,0xC3,0x03,0x02,0xC2,0xC6,0x06,
  42.     0x07,0xC7,0x05,0xC5,0xC4,0x04,0xCC,0x0C,0x0D,0xCD,
  43.     0x0F,0xCF,0xCE,0x0E,0x0A,0xCA,0xCB,0x0B,0xC9,0x09,
  44.     0x08,0xC8,0xD8,0x18,0x19,0xD9,0x1B,0xDB,0xDA,0x1A,
  45.     0x1E,0xDE,0xDF,0x1F,0xDD,0x1D,0x1C,0xDC,0x14,0xD4,
  46.     0xD5,0x15,0xD7,0x17,0x16,0xD6,0xD2,0x12,0x13,0xD3,
  47.     0x11,0xD1,0xD0,0x10,0xF0,0x30,0x31,0xF1,0x33,0xF3,
  48.     0xF2,0x32,0x36,0xF6,0xF7,0x37,0xF5,0x35,0x34,0xF4,
  49.     0x3C,0xFC,0xFD,0x3D,0xFF,0x3F,0x3E,0xFE,0xFA,0x3A,
  50.     0x3B,0xFB,0x39,0xF9,0xF8,0x38,0x28,0xE8,0xE9,0x29,
  51.     0xEB,0x2B,0x2A,0xEA,0xEE,0x2E,0x2F,0xEF,0x2D,0xED,
  52.     0xEC,0x2C,0xE4,0x24,0x25,0xE5,0x27,0xE7,0xE6,0x26,
  53.     0x22,0xE2,0xE3,0x23,0xE1,0x21,0x20,0xE0,0xA0,0x60,
  54.     0x61,0xA1,0x63,0xA3,0xA2,0x62,0x66,0xA6,0xA7,0x67,
  55.     0xA5,0x65,0x64,0xA4,0x6C,0xAC,0xAD,0x6D,0xAF,0x6F,
  56.     0x6E,0xAE,0xAA,0x6A,0x6B,0xAB,0x69,0xA9,0xA8,0x68,
  57.     0x78,0xB8,0xB9,0x79,0xBB,0x7B,0x7A,0xBA,0xBE,0x7E,
  58.     0x7F,0xBF,0x7D,0xBD,0xBC,0x7C,0xB4,0x74,0x75,0xB5,
  59.     0x77,0xB7,0xB6,0x76,0x72,0xB2,0xB3,0x73,0xB1,0x71,
  60.     0x70,0xB0,0x50,0x90,0x91,0x51,0x93,0x53,0x52,0x92,
  61.     0x96,0x56,0x57,0x97,0x55,0x95,0x94,0x54,0x9C,0x5C,
  62.     0x5D,0x9D,0x5F,0x9F,0x9E,0x5E,0x5A,0x9A,0x9B,0x5B,
  63.     0x99,0x59,0x58,0x98,0x88,0x48,0x49,0x89,0x4B,0x8B,
  64.     0x8A,0x4A,0x4E,0x8E,0x8F,0x4F,0x8D,0x4D,0x4C,0x8C,
  65.     0x44,0x84,0x85,0x45,0x87,0x47,0x46,0x86,0x82,0x42,
  66.     0x43,0x83,0x41,0x81,0x80,0x40
  67. };
  68.  
  69. /* CRCBUF  --  Calculate CRC-16 of BUFFLEN characters in BUFF.
  70.                The first character of BUFF must be nonzero.    */
  71.  
  72. unsigned short crc(unsigned char __far *buff, int bufflen)
  73. {
  74.     register unsigned int c, crc1, crc2;
  75.  
  76.     crc1 = crc2 = 0;
  77.     while (bufflen-- > 0) {
  78.         crc1 = low8[c = 0xFF & (*buff++ ^ crc1)] ^ crc2;
  79.         crc2 = high8[c];
  80.     }
  81.     return ((crc2 << 8) | (crc1 & 0xFF));
  82. }
  83.