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/*
* Copyright (c) 2008 Nicira Networks.
*
* Permission to use, copy, modify, and/or distribute this software for any
* purpose with or without fee is hereby granted, provided that the above
* copyright notice and this permission notice appear in all copies.
*
* THE SOFTWARE IS PROVIDED "AS IS" AND THE AUTHOR DISCLAIMS ALL WARRANTIES
* WITH REGARD TO THIS SOFTWARE INCLUDING ALL IMPLIED WARRANTIES OF
* MERCHANTABILITY AND FITNESS. IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR
* ANY SPECIAL, DIRECT, INDIRECT, OR CONSEQUENTIAL DAMAGES OR ANY DAMAGES
* WHATSOEVER RESULTING FROM LOSS OF USE, DATA OR PROFITS, WHETHER IN AN
* ACTION OF CONTRACT, NEGLIGENCE OR OTHER TORTIOUS ACTION, ARISING OUT OF
* OR IN CONNECTION WITH THE USE OR PERFORMANCE OF THIS SOFTWARE.
*/
#include <config.h>
#include "csum.h"
/* Returns the IP checksum of the 'n' bytes in 'data'. */
uint16_t
csum(const void *data, size_t n)
{
return csum_finish(csum_continue(0, data, n));
}
/* Adds the 16 bits in 'new' to the partial IP checksum 'partial' and returns
* the updated checksum. (To start a new checksum, pass 0 for 'partial'. To
* obtain the finished checksum, pass the return value to csum_finish().) */
uint32_t
csum_add16(uint32_t partial, uint16_t new)
{
return partial + new;
}
/* Adds the 32 bits in 'new' to the partial IP checksum 'partial' and returns
* the updated checksum. (To start a new checksum, pass 0 for 'partial'. To
* obtain the finished checksum, pass the return value to csum_finish().) */
uint32_t
csum_add32(uint32_t partial, uint32_t new)
{
return partial + (new >> 16) + (new & 0xffff);
}
/* Adds the 'n' bytes in 'data' to the partial IP checksum 'partial' and
* returns the updated checksum. (To start a new checksum, pass 0 for
* 'partial'. To obtain the finished checksum, pass the return value to
* csum_finish().) */
uint32_t
csum_continue(uint32_t partial, const void *data_, size_t n)
{
const uint16_t *data = data_;
for (; n > 1; n -= 2) {
partial = csum_add16(partial, *data++);
}
if (n) {
partial += *(uint8_t *) data;
}
return partial;
}
/* Returns the IP checksum corresponding to 'partial', which is a value updated
* by some combination of csum_add16(), csum_add32(), and csum_continue(). */
uint16_t
csum_finish(uint32_t partial)
{
return ~((partial & 0xffff) + (partial >> 16));
}
/* Returns the new checksum for a packet in which the checksum field previously
* contained 'old_csum' and in which a field that contained 'old_u16' was
* changed to contain 'new_u16'. */
uint16_t
recalc_csum16(uint16_t old_csum, uint16_t old_u16, uint16_t new_u16)
{
/* Ones-complement arithmetic is endian-independent, so this code does not
* use htons() or ntohs().
*
* See RFC 1624 for formula and explanation. */
uint16_t hc_complement = ~old_csum;
uint16_t m_complement = ~old_u16;
uint16_t m_prime = new_u16;
uint32_t sum = hc_complement + m_complement + m_prime;
uint16_t hc_prime_complement = sum + (sum >> 16);
return ~hc_prime_complement;
}
/* Returns the new checksum for a packet in which the checksum field previously
* contained 'old_csum' and in which a field that contained 'old_u32' was
* changed to contain 'new_u32'. */
uint16_t
recalc_csum32(uint16_t old_csum, uint32_t old_u32, uint32_t new_u32)
{
return recalc_csum16(recalc_csum16(old_csum, old_u32, new_u32),
old_u32 >> 16, new_u32 >> 16);
}
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