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mywiki:linux:ip_checksum_apis

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mywiki:linux:ip_checksum_apis [2015/05/08 09:32] – created supermywiki:linux:ip_checksum_apis [2019/09/15 18:55] (current) – external edit 127.0.0.1
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 } }
 </file> </file>
 +
 +
 +====== UDP Checksum calculation ======
 +<file c udp_checksum.c>
 +/* set tcp checksum: given IP header and its IP payload, ie, UDP header and its payload */
 +void compute_udp_checksum(struct iphdr *pIph, unsigned short *ipPayload)
 +{
 + register unsigned long sum = 0;
 + struct udphdr *udphdrp = (struct udphdr *)(ipPayload);
 + unsigned short udpLen = htons(udphdrp->len);
 + //the source ip
 + sum += (pIph->saddr >> 16) & 0xFFFF;
 + sum += (pIph->saddr) & 0xFFFF;
 + //the dest ip
 + sum += (pIph->daddr >> 16) & 0xFFFF;
 + sum += (pIph->daddr) & 0xFFFF;
 + //protocol and reserved: 17
 + sum += htons(IPPROTO_UDP);
 + //the length
 + sum += udphdrp->len;
 + //add the IP payload
 + //printf("add ip payload\n");
 + //initialize checksum to 0
 + udphdrp->check = 0;
 +
 + while (udpLen > 1) {
 + sum += * ipPayload++;
 + udpLen -= 2;
 + }
 +
 + //if any bytes left, pad the bytes and add
 + if (udpLen > 0) {
 + //printf("+++++++++++++++padding: %d\n", udpLen);
 + sum += ((*ipPayload)&htons(0xFF00));
 + }
 +
 + while (sum >> 16)
 + sum = (sum & 0xffff) + (sum >> 16);
 +
 + sum = ~sum;
 + //set computation result
 + udphdrp->check = ((unsigned short)sum == 0x0000) ? 0xFFFF : (unsigned short)sum;
 +}
 +</file>
 +
 +====== TCP Checksum calculation ======
 +<file c tcp_checksum.c>
 +/* set tcp checksum: given IP header and tcp segment */
 +void compute_tcp_checksum(struct iphdr *pIph, unsigned short *ipPayload)
 +{
 + register unsigned long sum = 0;
 + unsigned short tcpLen = ntohs(pIph->tot_len) - (pIph->ihl << 2);
 + struct tcphdr *tcphdrp = (struct tcphdr *)(ipPayload);
 + //add the pseudo header
 + //the source ip
 + sum += (pIph->saddr >> 16) & 0xFFFF;
 + sum += (pIph->saddr) & 0xFFFF;
 + //the dest ip
 + sum += (pIph->daddr >> 16) & 0xFFFF;
 + sum += (pIph->daddr) & 0xFFFF;
 + //protocol and reserved: 6
 + sum += htons(IPPROTO_TCP);
 + //the length
 + sum += htons(tcpLen);
 + //add the IP payload
 + //initialize checksum to 0
 + tcphdrp->check = 0;
 +
 + while (tcpLen > 1) {
 + sum += * ipPayload++;
 + tcpLen -= 2;
 + }
 +
 + //if any bytes left, pad the bytes and add
 + if (tcpLen > 0) {
 + sum += ((*ipPayload)&htons(0xFF00));
 + }
 +
 + //Fold 32-bit sum to 16 bits: add carrier to result
 + while (sum >> 16)
 + sum = (sum & 0xffff) + (sum >> 16);
 +
 + sum = ~sum;
 + //set computation result
 + tcphdrp->check = (unsigned short)sum;
 +}
 +</file>
 +
mywiki/linux/ip_checksum_apis.1431048758.txt.gz · Last modified: (external edit)