Ben Pfaff
116 lines
4.3 KiB
C
116 lines
4.3 KiB
C
/* Copyright (c) 2008 The Board of Trustees of The Leland Stanford
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* Junior University
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*
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* We are making the OpenFlow specification and associated documentation
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* (Software) available for public use and benefit with the expectation
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* that others will use, modify and enhance the Software and contribute
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* those enhancements back to the community. However, since we would
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* like to make the Software available for broadest use, with as few
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* restrictions as possible permission is hereby granted, free of
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* charge, to any person obtaining a copy of this Software to deal in
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* the Software under the copyrights without restriction, including
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* without limitation the rights to use, copy, modify, merge, publish,
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* distribute, sublicense, and/or sell copies of the Software, and to
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* permit persons to whom the Software is furnished to do so, subject to
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* the following conditions:
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*
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* The above copyright notice and this permission notice shall be
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* included in all copies or substantial portions of the Software.
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*
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* THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND,
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* EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF
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* MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND
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* NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS
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* BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN
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* ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN
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* CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
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* SOFTWARE.
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*
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* The name and trademarks of copyright holder(s) may NOT be used in
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* advertising or publicity pertaining to the Software or any
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* derivatives without specific, written prior permission.
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*/
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#include <config.h>
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#include "csum.h"
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/* Returns the IP checksum of the 'n' bytes in 'data'. */
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uint16_t
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csum(const void *data, size_t n)
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{
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return csum_finish(csum_continue(0, data, n));
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}
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/* Adds the 16 bits in 'new' to the partial IP checksum 'partial' and returns
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* the updated checksum. (To start a new checksum, pass 0 for 'partial'. To
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* obtain the finished checksum, pass the return value to csum_finish().) */
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uint32_t
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csum_add16(uint32_t partial, uint16_t new)
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{
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return partial + new;
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}
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/* Adds the 32 bits in 'new' to the partial IP checksum 'partial' and returns
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* the updated checksum. (To start a new checksum, pass 0 for 'partial'. To
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* obtain the finished checksum, pass the return value to csum_finish().) */
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uint32_t
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csum_add32(uint32_t partial, uint32_t new)
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{
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return partial + (new >> 16) + (new & 0xffff);
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}
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/* Adds the 'n' bytes in 'data' to the partial IP checksum 'partial' and
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* returns the updated checksum. (To start a new checksum, pass 0 for
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* 'partial'. To obtain the finished checksum, pass the return value to
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* csum_finish().) */
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uint32_t
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csum_continue(uint32_t partial, const void *data_, size_t n)
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{
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const uint16_t *data = data_;
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for (; n > 1; n -= 2) {
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partial = csum_add16(partial, *data++);
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}
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if (n) {
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partial += *(uint8_t *) data;
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}
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return partial;
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}
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/* Returns the IP checksum corresponding to 'partial', which is a value updated
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* by some combination of csum_add16(), csum_add32(), and csum_continue(). */
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uint16_t
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csum_finish(uint32_t partial)
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{
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return ~((partial & 0xffff) + (partial >> 16));
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}
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/* Returns the new checksum for a packet in which the checksum field previously
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* contained 'old_csum' and in which a field that contained 'old_u16' was
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* changed to contain 'new_u16'. */
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uint16_t
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recalc_csum16(uint16_t old_csum, uint16_t old_u16, uint16_t new_u16)
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{
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/* Ones-complement arithmetic is endian-independent, so this code does not
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* use htons() or ntohs().
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*
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* See RFC 1624 for formula and explanation. */
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uint16_t hc_complement = ~old_csum;
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uint16_t m_complement = ~old_u16;
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uint16_t m_prime = new_u16;
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uint32_t sum = hc_complement + m_complement + m_prime;
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uint16_t hc_prime_complement = sum + (sum >> 16);
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return ~hc_prime_complement;
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}
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/* Returns the new checksum for a packet in which the checksum field previously
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* contained 'old_csum' and in which a field that contained 'old_u32' was
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* changed to contain 'new_u32'. */
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uint16_t
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recalc_csum32(uint16_t old_csum, uint32_t old_u32, uint32_t new_u32)
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{
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return recalc_csum16(recalc_csum16(old_csum, old_u32, new_u32),
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old_u32 >> 16, new_u32 >> 16);
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}
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