The sample code provided is in the C programming language. (See also ISO 3309 and ITU-T V.42 for a formal specification.)
/* table of crc's of all 8-bit messages */ unsigned long crc_table[256]; /* Flag: has the table been computed? Initially false. */ int crc_table_computed = 0; /* make the table for a fast crc */ void make_crc_table(void) { unsigned long c; int n, k; for (n = 0; n < 256; n++) { c = (unsigned long) n; for (k = 0; k < 8; k++) c = (c & 1) ? (0xedb88320L ^ (c >> 1)) : (c >> 1); crc_table[n] = c; } crc_table_computed = 1; } /* update a running crc with the bytes buf[0..len-1]--the crc should be initialized to all 1's, and the transmitted value is the 1's complement of the final running crc (see the crc() routine below)). */ unsigned long update_crc(unsigned long crc, unsigned char *buf, int len) { unsigned long c = crc; unsigned char *p = buf; int n = len; if (!crc_table_computed) make_crc_table(); if (n > 0) do { c = crc_table[(c ^ (*p++)) & 0xff] ^ (c >> 8); } while (--n); return c; } /* return the crc of the bytes buf[0..len-1] */ unsigned long crc(unsigned char *buf, int len) { if (!crc_table_computed) make_crc_table(); return update_crc(0xffffffffL, buf, len) ^ 0xffffffffL; }