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/*
* Copyright (c) 2008, 2009, 2010, 2011 Nicira Networks.
*
* Licensed under the Apache License, Version 2.0 (the "License");
* you may not use this file except in compliance with the License.
* You may obtain a copy of the License at:
*
* http://www.apache.org/licenses/LICENSE-2.0
*
* Unless required by applicable law or agreed to in writing, software
* distributed under the License is distributed on an "AS IS" BASIS,
* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
* See the License for the specific language governing permissions and
* limitations under the License.
*/
#include <config.h>
#include "csum.h"
#include "unaligned.h"
#ifndef __CHECKER__
/* Returns the IP checksum of the 'n' bytes in 'data'.
*
* The return value has the same endianness as the data. That is, if 'data'
* consists of a packet in network byte order, then the return value is a value
* in network byte order, and if 'data' consists of a data structure in host
* byte order, then the return value is in host byte order. */
ovs_be16
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, ovs_be16 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, ovs_be32 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 ovs_be16 *data = data_;
for (; n > 1; n -= 2, data++) {
partial = csum_add16(partial, get_unaligned_be16(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().
*
* The return value has the same endianness as the checksummed data. That is,
* if the data consist of a packet in network byte order, then the return value
* is a value in network byte order, and if the data are a data structure in
* host byte order, then the return value is in host byte order. */
ovs_be16
csum_finish(uint32_t partial)
{
while (partial >> 16) {
partial = (partial & 0xffff) + (partial >> 16);
}
return ~partial;
}
/* 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'. */
ovs_be16
recalc_csum16(ovs_be16 old_csum, ovs_be16 old_u16, ovs_be16 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;
return csum_finish(sum);
}
/* 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'. */
ovs_be16
recalc_csum32(ovs_be16 old_csum, ovs_be32 old_u32, ovs_be32 new_u32)
{
return recalc_csum16(recalc_csum16(old_csum, old_u32, new_u32),
old_u32 >> 16, new_u32 >> 16);
}
#else /* __CHECKER__ */
/* Making sparse happy with these functions also makes them unreadable, so
* don't bother to show it their implementations. */
#endif
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