Cyclic Redundancy Check (crc)

A cyclic redundancy check (CRC) is, in essence, a strong algebraic error detection code that computes a key on a block of data using base-2 polynomials. While it is a strong error-detection method, a CRC is not an error-correction code. Here is a simple example:

#include <liquid/liquid.h>

int main() {
    // initialize data array
    unsigned char data[4] = {0x25, 0x62, 0x3F, 0x52};
    crc_scheme scheme = LIQUID_CRC_32;

    // compute CRC on original data
    unsigned char key = crc_generate_key(scheme, data, 4);

    // ... channel ...

    // validate (received) message
    int valid_data = crc_validate_message(scheme, data, 4, key);
}

Also available for error detection in liquid is a checksum. A checksum is a simple way to validate data received through un-reliable means (e.g. a noisy channel). A checksum is, in essence, a weak error detection code that simply counts the number of ones in a block of data (modulo 256). The limitation, however, is that multiple bit errors might result in a false positive validation of the corrupted data. The checksum is not a strong an error detection scheme as the cyclic redundancy check.[ref:tab-crc-codecs] lists the available codecs and gives a brief description for each.

Table [tab-crc-codecs]. Error-detection codecs available in liquid

For a detailed example program, see examples/crc_example.c in the main liquid directory.