/* Simple public domain implementation of the standard CRC32 checksum. * Outputs the checksum for each file given as a command line argument. * Invalid file names and files that cause errors are silently skipped. * The program reads from stdin if it is called with no arguments. */ #include #include #include static uint32_t crc32_for_byte(uint32_t r) { for(int j = 0; j < 8; ++j) r = (r & 1? 0: (uint32_t)0xEDB88320L) ^ r >> 1; return r ^ (uint32_t)0xFF000000L; } void crc32(const void *data, uint32_t n_bytes, uint32_t* crc) { static uint32_t table[0x100]; if(!*table) for(uint32_t i = 0; i < 0x100; ++i) table[i] = crc32_for_byte(i); for(uint32_t i = 0; i < n_bytes; ++i) *crc = table[(uint8_t)*crc ^ ((uint8_t*)data)[i]] ^ *crc >> 8; } uint32_t crc32_buf(const void *buf, uint32_t n_bytes) { uint32_t crc = 0; crc32(buf, n_bytes, &crc); return crc; }