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58 lines
1.7 KiB
58 lines
1.7 KiB
/*
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* Copyright (C) 2020 The Android Open Source Project
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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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#ifndef ANALYZER_PSEUDORANDOM_H
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#define ANALYZER_PSEUDORANDOM_H
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#include <cctype>
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class PseudoRandom {
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public:
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PseudoRandom(int64_t seed = 99887766)
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: mSeed(seed)
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{}
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/**
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* Returns the next random double from -1.0 to 1.0
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*
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* @return value from -1.0 to 1.0
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*/
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double nextRandomDouble() {
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return nextRandomInteger() * (0.5 / (((int32_t)1) << 30));
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}
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/** Calculate random 32 bit number using linear-congruential method
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* with known real-time performance.
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*/
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int32_t nextRandomInteger() {
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#if __has_builtin(__builtin_mul_overflow) && __has_builtin(__builtin_add_overflow)
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int64_t prod;
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// Use values for 64-bit sequence from MMIX by Donald Knuth.
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__builtin_mul_overflow(mSeed, (int64_t)6364136223846793005, &prod);
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__builtin_add_overflow(prod, (int64_t)1442695040888963407, &mSeed);
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#else
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mSeed = (mSeed * (int64_t)6364136223846793005) + (int64_t)1442695040888963407;
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#endif
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return (int32_t) (mSeed >> 32); // The higher bits have a longer sequence.
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}
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private:
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int64_t mSeed;
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};
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#endif //ANALYZER_PSEUDORANDOM_H
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