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/* SPDX-License-Identifier: BSD-3-Clause OR GPL-2.0-or-later */
#include <commonlib/bsd/ipchksum.h>
/* See RFC 1071 for mathematical explanations of why we can first sum in a larger register and
then narrow down, why we don't need to worry about endianness, etc. */
uint16_t ipchksum(const void *data, size_t size)
{
const uint8_t *p1 = data;
unsigned long wide_sum = 0;
uint32_t sum = 0;
size_t i = 0;
while (wide_sum) {
sum += wide_sum & 0xFFFF;
wide_sum >>= 16;
}
sum = (sum & 0xFFFF) + (sum >> 16);
for (; i < size; i++) {
uint32_t v = p1[i];
if (i % 2)
v <<= 8;
sum += v;
/* Doing this unconditionally seems to be faster. */
sum = (sum & 0xFFFF) + (sum >> 16);
}
return (uint16_t)~sum;
}
uint16_t ipchksum_add(size_t offset, uint16_t first, uint16_t second)
{
first = ~first;
second = ~second;
/*
* Since the checksum is calculated in 16-bit chunks, if the offset at which
* the data covered by the second checksum would start (if both data streams
* came one after the other) is odd, that means the second stream starts in
* the middle of a 16-bit chunk. This means the second checksum is byte
* swapped compared to what we need it to be, and we must swap it back.
*/
if (offset % 2)
second = (second >> 8) | (second << 8);
uint32_t sum = first + second;
sum = (sum & 0xFFFF) + (sum >> 16);
return (uint16_t)~sum;
}
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