8bb54b04ef
FYI: find ortools \( -type d -name .git -prune \) -o -type f -print0 | xargs -0 sed -i 's/\(Copyright 2010\)-2018/\1-2021/g'
54 lines
2.0 KiB
C++
54 lines
2.0 KiB
C++
// Copyright 2010-2021 Google LLC
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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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#ifndef OR_TOOLS_BASE_THOROUGH_HASH_H_
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#define OR_TOOLS_BASE_THOROUGH_HASH_H_
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#include "ortools/base/integral_types.h"
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namespace operations_research {
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inline uint64_t MixTwoUInt64(uint64_t fp1, uint64_t fp2) {
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// Two big prime numbers.
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const uint64_t kMul1 = 0xc6a4a7935bd1e995ULL;
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const uint64_t kMul2 = 0x228876a7198b743ULL;
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uint64_t a = fp1 * kMul1 + fp2 * kMul2;
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// Note: The following line also makes sure we never return 0 or 1, because we
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// will only add something to 'a' if there are any MSBs (the remaining bits
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// after the shift) being 0, in which case wrapping around would not happen.
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return a + (~a >> 47);
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}
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// This should be better (collision-wise) than the default hash<string>, without
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// being much slower. It never returns 0 or 1.
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inline uint64_t ThoroughHash(const char* bytes, size_t len) {
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// Some big prime numer.
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uint64_t fp = 0xa5b85c5e198ed849ULL;
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const char* end = bytes + len;
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while (bytes + 8 <= end) {
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fp = MixTwoUInt64(fp, *(reinterpret_cast<const uint64_t*>(bytes)));
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bytes += 8;
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}
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// Note: we don't care about "consistency" (little or big endian) between
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// the bulk and the suffix of the message.
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uint64_t last_bytes = 0;
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while (bytes < end) {
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last_bytes += *bytes;
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last_bytes <<= 8;
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bytes++;
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}
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return MixTwoUInt64(fp, last_bytes);
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}
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} // namespace operations_research
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#endif // OR_TOOLS_BASE_THOROUGH_HASH_H_
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