Отображение CRC32 в генераторе Ethernet-пакетов Mausezahn / How to show SW-generated mimic of HW-generated CRC32 for Ethernet adapters by Mausezahn

Warning: This does not work when padding bytes added, because they unknown. (fixed)

How to modify layer1.c:

(i am sorry, code correct displaying and highlighting still impossible here)

I extremely tired to fight with wordpress, so please manually replace symmetric unicode double quotes to normal 0x22 quotes manually. Only i need is to display copyable source code here. But it impossible at all with wordpress.

diff -u layer1.c.old layer1.c

--- layer1.c.old	2009-11-23 00:11:38.000000000 +0200
+++ layer1.c	2014-02-28 11:42:46.000000000 +0300
@@ -60,10 +60,19 @@
      err_buf[LIBNET_ERRBUF_SIZE],
      message[MAX_PAYLOAD_SIZE*3];
      
-   u_int8_t       bytestring[MAX_PAYLOAD_SIZE];
+   u_int8_t       bytestring[MAX_PAYLOAD_SIZE+6+6+2];
    libnet_ptag_t  t;
    libnet_t       *l;
 
+   int sum;
+   u_long crc;
+   unsigned int crc_table[] =
+     {
+       0x4DBDF21C, 0x500AE278, 0x76D3D2D4, 0x6B64C2B0,
+       0x3B61B38C, 0x26D6A3E8, 0x000F9344, 0x1DB88320,
+       0xA005713C, 0xBDB26158, 0x9B6B51F4, 0x86DC4190,
+       0xD6D930AC, 0xCB6E20C8, 0xEDB71064, 0xF0000000
+     };
    
 	
    if (tx.dot1Q)
@@ -294,6 +303,35 @@
 		       fprintf(stderr, " mz/send_eth: %s", libnet_geterror(l));
 		       return -1;
 		    }
+
+		    // Calculate sum and crc32. WARNING, all bytes must be defined while generating packet.
+		    bytestring[0] = tx.eth_dst[0];
+		    bytestring[1] = tx.eth_dst[1];
+		    bytestring[2] = tx.eth_dst[2];
+		    bytestring[3] = tx.eth_dst[3];
+		    bytestring[4] = tx.eth_dst[4];
+		    bytestring[5] = tx.eth_dst[5];
+		    bytestring[6] = tx.eth_src[0];
+		    bytestring[7] = tx.eth_src[1];
+		    bytestring[8] = tx.eth_src[2];
+		    bytestring[9] = tx.eth_src[3];
+		    bytestring[10] = tx.eth_src[4];
+		    bytestring[11] = tx.eth_src[5];
+		    bytestring[12] = (tx.eth_type>>8) & 0xff;
+		    bytestring[13] = tx.eth_type & 0xff;
+		    for (i=0; i<tx.eth_payload_s; i++) bytestring[i+6+6+2]=tx.eth_payload[i];
+		 
+		    sum=0;
+		    crc=0;
+		    for (i=0; i<tx.eth_payload_s+6+6+2; i++) {
+		      sum = (sum + bytestring[i]) & 0xff;
+
+		      //  http://www.edaboard.com/thread120700.html
+		      crc = (crc >> 4) ^ crc_table[(crc ^ (bytestring[i] >> 0)) & 0x0F]; /* lower nibble */
+		      crc = (crc >> 4) ^ crc_table[(crc ^ (bytestring[i] >> 4)) & 0x0F]; /* upper nibble */
+		 //printf("%02x ",(uint)bytestring[i]);
+		    }
+		    printf("  send: Len=%d Sum=%d CRC32=%08lx (%02x %02x %02x %02x on wire) \n", tx.eth_payload_s+6+6+2, sum, crc, (uint)(crc & 0xff), (uint)(crc>>8 & 0xff), (uint)(crc>>16 & 0xff), (uint)(crc>>24 & 0xff));
 		  
 		  if (verbose) 
 		    {