crc 循环冗余校验码.c

CRC 循环冗余校验码,C语言写的,

#include <stdio.h>
#include <stdlib.h>

typedef unsigned short u16;
#define CRC16_POLYNOMIAL 0x8408  /*  x**0 + x**5 + x**12 + x**16 */
#define PPPINITFCS16    0xffff  /* Initial FCS value */
#define PPPGOODFCS16    0xf0b8  /* Good final FCS value */

static u16 crc16_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
   };

/* CRC16 lookup table as calculated by the table generator. */
void Make_Crctable(void)
   {
       unsigned int b, v;
       int i;

       printf("typedef unsigned short u16;\n");
       printf("static u16 crc16_table[256] = {");
       for (b = 0; ; ) {
           if (b % 8 == 0)
               printf("\n");

           v = b;
           for (i = 8; i--; )
               v = v & 1 ? (v >> 1) ^ CRC16_POLYNOMIAL : v >> 1;
           printf("\t0x%04x", v & 0xFFFF);
           crc16_table[b] = v & 0xFFFF;
           if (++b == 256)
               break;
           printf(",");
       }
       printf("\n};\n");
   }
/* Calculate a new fcs given the current fcs and the new data. */
u16 pppfcs16(u16 fcs, unsigned char *cp, int len)
   {
   while (len--)
       fcs = (fcs >> 8) ^ crc16_table[(fcs ^ *cp++) & 0xff];
   return (fcs);
   }

/* How to use the fcs */
void tryfcs16(unsigned char *cp, int len)
   {
       u16 trialfcs;
       /* add on output */
       trialfcs = pppfcs16( PPPINITFCS16, cp, len );
       trialfcs ^= 0xffff;                 /* complement */
       cp[len] = (trialfcs & 0x00ff);      /* least significant byte first */
       cp[len+1] = ((trialfcs >> 8) & 0x00ff);
       printf("The crc16 is: %x",cp[len]);
       printf("%x\n",cp[len+1]);
      /* check on input */
       trialfcs = pppfcs16( PPPINITFCS16, cp, len + 2 );
       printf("The test result is: %x\n",trialfcs);
       printf("The Crect result should be: %x\n",PPPGOODFCS16);
       if ( trialfcs == PPPGOODFCS16 )
           printf("Good FCS\n");
       else
           printf("Bad FCS\n");
   }

int main(int argc, char *argv[])
{
  char *s;
  char c;
  Make_Crctable();
  while(1)
      {
      printf("Please input the test string: \n");
      scanf("%s",s);
      printf("The input string is: %s\n",s);
      printf("The string length is :%d\n",strlen(s));
      tryfcs16(s,strlen(s));
      printf("Press <e>xit and <enter> exit program\n" );
      printf("Press any others key and <enter> continue\n");
      scanf("%s",s);
      c=*s;
      if(c == 'e') break;
      }
  return 0;
}