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//
// crc_example.c
//
// Cyclic redundancy check (CRC) example. This example demonstrates
// how a CRC can be used to validate data received through un-reliable
// means (e.g. a noisy channel). A CRC is, in essence, a strong
// algebraic error detection code that computes a key on a block of data
// using base-2 polynomials.
// SEE ALSO: checksum_example.c
// fec_example.c
//
#include <stdio.h>
#include <stdlib.h>
#include <getopt.h>
#include "liquid.h"
// print usage/help message
void usage()
{
printf("crc_example [options]\n");
printf(" u/h : print usage\n");
printf(" n : input data size (number of uncoded bytes)\n");
printf(" v : checking scheme, (crc32 default):\n");
liquid_print_crc_schemes();
}
int main(int argc, char*argv[])
{
// options
unsigned int n = 32; // data length (bytes)
crc_scheme check = LIQUID_CRC_32; // error-detection scheme
int dopt;
while((dopt = getopt(argc,argv,"uhn:v:")) != EOF){
switch (dopt) {
case 'h':
case 'u': usage(); return 0;
case 'n': n = atoi(optarg); break;
case 'v':
check = liquid_getopt_str2crc(optarg);
if (check == LIQUID_CRC_UNKNOWN) {
fprintf(stderr,"error: unknown/unsupported error-detection scheme \"%s\"\n\n",optarg);
exit(1);
}
break;
default:
exit(1);
}
}
// validate input
unsigned int i;
// initialize data array, leaving space for key at the end
unsigned char data[n+4];
for (i=0; i<n; i++)
data[i] = rand() & 0xff;
// append key to data message
crc_append_key(check, data, n);
// check uncorrupted data
printf("testing uncorrupted data... %s\n", crc_check_key(check, data, n) ? "pass" : "FAIL");
// corrupt message and check data again
data[0]++;
printf("testing corrupted data... %s\n", crc_check_key(check, data, n) ? "pass" : "FAIL (ok)");
printf("done.\n");
return 0;
}
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