Free Software Foundation, Inc., 59 Temple Place - Suite 330,
Boston, MA 02111-1307, USA.
- For the actual CRC code:
+ For the actual CRC-32 code:
Copyright abandoned; this code is in the public domain.
Provided to GNUnet by peter@horizon.com
*/
/**
* @file util/crypto_crc.c
- * @brief implementation of CRC32
+ * @brief implementation of CRC16 and CRC32
* @author Christian Grothoff
*/
-
#include "platform.h"
#include "gnunet_common.h"
#include "gnunet_crypto_lib.h"
/*
* This routine writes each crc_table entry exactly once,
- * with the ccorrect final value. Thus, it is safe to call
+ * with the correct final value. Thus, it is safe to call
* even on a table that someone else is using concurrently.
*/
static void
return crc;
}
+
+/**
+ * Perform an incremental step in a CRC16 (for TCP/IP) calculation.
+ *
+ * @param sum current sum, initially 0
+ * @param buf buffer to calculate CRC over (must be 16-bit aligned)
+ * @param len number of bytes in hdr, must be multiple of 2
+ * @return updated crc sum (must be subjected to GNUNET_CRYPTO_crc16_finish to get actual crc16)
+ */
+uint32_t
+GNUNET_CRYPTO_crc16_step (uint32_t sum, const void *buf, size_t len)
+{
+ const uint16_t *hdr = buf;
+ for (; len >= 2; len -= 2)
+ sum += *(hdr++);
+ if (len == 1)
+ sum += (*hdr) & ntohs(0xFF00);
+ return sum;
+}
+
+
+/**
+ * Convert results from GNUNET_CRYPTO_crc16_step to final crc16.
+ *
+ * @param sum cummulative sum
+ * @return crc16 value
+ */
+uint16_t
+GNUNET_CRYPTO_crc16_finish (uint32_t sum)
+{
+ sum = (sum >> 16) + (sum & 0xFFFF);
+ sum += (sum >> 16);
+
+ return ~sum;
+}
+
+
+/**
+ * Calculate the checksum of a buffer in one step.
+ *
+ * @param buf buffer to calculate CRC over (must be 16-bit aligned)
+ * @param len number of bytes in hdr, must be multiple of 2
+ * @return crc16 value
+ */
+uint16_t
+GNUNET_CRYPTO_crc16_n (const void *buf, size_t len)
+{
+ const uint16_t *hdr = buf;
+ uint32_t sum = GNUNET_CRYPTO_crc16_step (0, hdr, len);
+
+ return GNUNET_CRYPTO_crc16_finish (sum);
+}
+
+
+
/* end of crypto_crc.c */