/* * C Implementation: crc32 * * code from http://www.w3.org/TR/PNG/#D-CRCAppendix * */ /* Table of CRCs of all 8-bit messages. */ static unsigned long crc_table[256]; /* Flag: has the table been computed? Initially false. */ static int crc_table_computed = 0; /* Make the table for a fast CRC. */ static 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++) { if (c & 1) c = 0xedb88320L ^ (c >> 1); else c = 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). */ static unsigned long update_crc(unsigned long crc, unsigned char *buf, int len) { unsigned long c = crc; int n; if (!crc_table_computed) make_crc_table(); for (n = 0; n < len; n++) { c = crc_table[(c ^ buf[n]) & 0xff] ^ (c >> 8); } return c; } /* Return the CRC of the bytes buf[0..len-1]. */ unsigned long mpc_crc32(unsigned char *buf, int len) { return update_crc(0xffffffffL, buf, len) ^ 0xffffffffL; }