mirror of
https://github.com/sheumann/hush.git
synced 2024-11-09 02:09:01 +00:00
37 lines
867 B
C
37 lines
867 B
C
/*
|
|
* 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(uint16_t *addr, int nleft)
|
|
{
|
|
/*
|
|
* 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;
|
|
}
|