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31 lines
692 B
C
31 lines
692 B
C
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#ifndef __IP_HELPER_H__
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#define __IP_HELPER_H__
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#include <linux/ip.h>
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/**
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* IP checksum calculation.
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* Following RFC 1071.
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* In essence 1's complement of 16-bit groups.
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* Taken from my own library https://github.com/h3xduck/RawTCP_Lib/blob/master/src/packet.c
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*/
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static __always_inline unsigned short checksum(unsigned short *addr, int nbytes){
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long sum = 0;
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unsigned short checksum;
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while(nbytes>1){
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sum += (unsigned short) *addr++;
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nbytes -= 2;
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}
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if(nbytes>0){
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sum +=htons((unsigned char)*addr);
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}
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while (sum>>16){
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sum = (sum & 0xffff) + (sum >> 16);
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}
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checksum = ~sum;
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return checksum;
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}
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#endif
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