56 lines
1.2 KiB
C
56 lines
1.2 KiB
C
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/* Taken from Etherboot */
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#include "libopenbios/ipchecksum.h"
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unsigned short ipchksum(const void *data, unsigned long length)
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{
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unsigned long sum;
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unsigned long i;
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const unsigned char *ptr;
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union {
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unsigned char byte[2];
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unsigned short word;
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} u;
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/* In the most straight forward way possible,
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* compute an ip style checksum.
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*/
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sum = 0;
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ptr = data;
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for(i = 0; i < length; i++) {
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unsigned long value;
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value = ptr[i];
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if (i & 1) {
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value <<= 8;
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}
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/* Add the new value */
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sum += value;
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/* Wrap around the carry */
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if (sum > 0xFFFF) {
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sum = (sum + (sum >> 16)) & 0xFFFF;
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}
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}
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u.byte[0] = (unsigned char) sum;
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u.byte[1] = (unsigned char) (sum >> 8);
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return (unsigned short) ~u.word;
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}
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unsigned short add_ipchksums(unsigned long offset, unsigned short sum, unsigned short new)
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{
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unsigned long checksum;
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sum = ~sum & 0xFFFF;
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new = ~new & 0xFFFF;
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if (offset & 1) {
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/* byte swap the sum if it came from an odd offset
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* since the computation is endian independant this
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* works.
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*/
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new = (new << 8) | (new >> 8);
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}
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checksum = sum + new;
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if (checksum > 0xFFFF) {
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checksum -= 0xFFFF;
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}
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return (~checksum) & 0xFFFF;
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}
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