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b63e3bbc18
It is needed for the classifier partitioning optimization. This commit only reintroduces the parts that are actually needed. Signed-off-by: Ben Pfaff <blp@nicira.com>
40 lines
1.3 KiB
C
40 lines
1.3 KiB
C
/*
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* Copyright (c) 2008, 2009, 2010, 2011, 2013 Nicira, Inc.
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*
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* Licensed under the Apache License, Version 2.0 (the "License");
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* you may not use this file except in compliance with the License.
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* You may obtain a copy of the License at:
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*
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* http://www.apache.org/licenses/LICENSE-2.0
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*
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* Unless required by applicable law or agreed to in writing, software
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* distributed under the License is distributed on an "AS IS" BASIS,
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* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
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* See the License for the specific language governing permissions and
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* limitations under the License.
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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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#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 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) % (N_TAG_BITS - 1);
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y += y >= x;
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return (1u << x) | (1u << y);
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}
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