49 lines
1.2 KiB
C
49 lines
1.2 KiB
C
#include <netutil/checksum.h>
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#include <netutil/htons.h>
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static uint16_t
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lwip_standard_chksum(void *dataptr, uint16_t len)
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{
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uint32_t acc;
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uint16_t src;
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uint8_t *octetptr;
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acc = 0;
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/* dataptr may be at odd or even addresses */
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octetptr = (uint8_t*)dataptr;
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while (len > 1) {
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/* declare first octet as most significant
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thus assume network order, ignoring host order */
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src = (*octetptr) << 8;
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octetptr++;
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/* declare second octet as least significant */
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src |= (*octetptr);
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octetptr++;
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acc += src;
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len -= 2;
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}
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if (len > 0) {
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/* accumulate remaining octet */
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src = (*octetptr) << 8;
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acc += src;
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}
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/* add deferred carry bits */
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acc = (acc >> 16) + (acc & 0x0000ffffUL);
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if ((acc & 0xffff0000UL) != 0) {
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acc = (acc >> 16) + (acc & 0x0000ffffUL);
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}
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/* This maybe a little confusing: reorder sum using htons()
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instead of ntohs() since it has a little less call overhead.
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The caller must invert bits for Internet sum ! */
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return htons((uint16_t)acc);
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};
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/**
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* Calculate a short such that ret + dataptr[..] becomes 0
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*/
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uint16_t inet_checksum(void *dataptr, uint16_t len)
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{
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return ~lwip_standard_chksum(dataptr, len);
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};
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