| /* |
| * 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; |
| } |