X-Git-Url: https://git.librecmc.org/?a=blobdiff_plain;f=src%2Futil%2Fcrypto_crc.c;h=ea50b636c0913e4fcf1761abf485db1e70366686;hb=72c8645af31896829b674b575c5375706f362a30;hp=5920ddc938425444259683cde39306ccabce8568;hpb=d9d94d0e53d26af75ec8241383d166544ebd79f3;p=oweals%2Fgnunet.git

diff --git a/src/util/crypto_crc.c b/src/util/crypto_crc.c
index 5920ddc93..ea50b636c 100644
--- a/src/util/crypto_crc.c
+++ b/src/util/crypto_crc.c
@@ -17,17 +17,16 @@
      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"
@@ -51,7 +50,7 @@ static uLong crc_table[256];
 
 /*
  * 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
@@ -66,12 +65,12 @@ crc_init ()
   once = 1;
   crc_table[0] = 0;
   for (i = 128; i; i >>= 1)
-    {
-      h = (h >> 1) ^ ((h & 1) ? POLYNOMIAL : 0);
-      /* h is now crc_table[i] */
-      for (j = 0; j < 256; j += 2 * i)
-	crc_table[i + j] = crc_table[j] ^ h;
-    }
+  {
+    h = (h >> 1) ^ ((h & 1) ? POLYNOMIAL : 0);
+    /* h is now crc_table[i] */
+    for (j = 0; j < 256; j += 2 * i)
+      crc_table[i + j] = crc_table[j] ^ h;
+  }
 }
 
 /*
@@ -113,4 +112,59 @@ GNUNET_CRYPTO_crc32_n (const void *buf, size_t len)
   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 */