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/*
* Checksum routine for Internet Protocol family headers (C Version)
*
* Licensed under GPLv2, see file LICENSE in this source tree.
*/
#include "libbb.h"
uint16_t FAST_FUNC inet_cksum(const void *ptr, int nleft)
{
const uint16_t *addr = ptr;
/*
* Our algorithm is simple, using a 32 bit accumulator,
* we add sequential 16 bit words to it, and at the end, fold
* back all the carry bits from the top 16 bits into the lower
* 16 bits.
*/
unsigned sum = 0;
while (nleft > 1) {
sum += *addr++;
nleft -= 2;
}
/* Mop up an odd byte, if necessary */
if (nleft == 1) {
if (BB_LITTLE_ENDIAN)
sum += *(uint8_t*)addr;
else
sum += *(uint8_t*)addr << 8;
}
/* Add back carry outs from top 16 bits to low 16 bits */
sum = (sum >> 16) + (sum & 0xffff); /* add hi 16 to low 16 */
sum += (sum >> 16); /* add carry */
return (uint16_t)~sum;
}
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