Mikio Hara
100 lines
3.5 KiB
C
100 lines
3.5 KiB
C
/* Copyright (c) 2008, 2009 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 "tag.h"
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#include <limits.h>
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#include "random.h"
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#include "type-props.h"
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#include "util.h"
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#define N_TAG_BITS (CHAR_BIT * sizeof(tag_type))
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BUILD_ASSERT_DECL(IS_POW2(N_TAG_BITS));
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#define LOG2_N_TAG_BITS (N_TAG_BITS == 32 ? 5 : N_TAG_BITS == 64 ? 6 : 0)
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BUILD_ASSERT_DECL(LOG2_N_TAG_BITS > 0);
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/* Returns a randomly selected tag. */
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tag_type
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tag_create_random(void)
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{
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int x, y;
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do {
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uint16_t r = random_uint16();
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x = r & (N_TAG_BITS - 1);
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y = r >> (16 - LOG2_N_TAG_BITS);
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} while (x == y);
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return (1u << x) | (1u << y);
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}
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/* Returns a tag deterministically generated from 'seed'.
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*
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* 'seed' should have data in all of its bits; if it has data only in its
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* low-order bits then the resulting tags will be poorly distributed. Use a
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* hash function such as hash_bytes() to generate 'seed' if necessary. */
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tag_type
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tag_create_deterministic(uint32_t seed)
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{
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int x = seed & (N_TAG_BITS - 1);
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int y = (seed >> LOG2_N_TAG_BITS) % 31;
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y += y >= x;
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return (1u << x) | (1u << y);
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}
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/* Initializes 'set' as an empty tag set. */
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void
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tag_set_init(struct tag_set *set)
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{
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memset(set, 0, sizeof *set);
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}
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/* Adds 'tag' to 'set'. */
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void
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tag_set_add(struct tag_set *set, tag_type tag)
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{
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if (tag && (!tag_is_valid(tag) || !tag_set_intersects(set, tag))) {
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/* XXX We could do better by finding the set member to which we would
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* add the fewest number of 1-bits. This would reduce the amount of
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* ambiguity, since e.g. three 1-bits match 3 * 2 / 2 = 3 unique tags
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* whereas four 1-bits match 4 * 3 / 2 = 6 unique tags. */
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tag_type *t = &set->tags[set->n++ % TAG_SET_SIZE];
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*t |= tag;
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if (*t == TYPE_MAXIMUM(tag_type)) {
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set->tags[0] = *t;
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}
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set->total |= tag;
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}
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}
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