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PojavLauncherTeam
GitHub Repository: PojavLauncherTeam/mobile
 Path: blob/master/src/hotspot/share/jfr/utilities/jfrRandom.inline.hpp
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/*

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 * Copyright (c) 2020, Oracle and/or its affiliates. All rights reserved.

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 * Copyright (c) 2018, Google and/or its affiliates. All rights reserved.

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 * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.

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 *

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 * This code is free software; you can redistribute it and/or modify it

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 * under the terms of the GNU General Public License version 2 only, as

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 * published by the Free Software Foundation.

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 *

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 * This code is distributed in the hope that it will be useful, but WITHOUT

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 * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or

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 * FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License

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 * version 2 for more details (a copy is included in the LICENSE file that

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 * accompanied this code).

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 *

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 * You should have received a copy of the GNU General Public License version

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 * 2 along with this work; if not, write to the Free Software Foundation,

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 * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.

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 *

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 * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA

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 * or visit www.oracle.com if you need additional information or have any

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 * questions.

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 *

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 */

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#ifndef SHARE_JFR_UTILITIES_JFRRANDOM_INLINE_HPP

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#define SHARE_JFR_UTILITIES_JFRRANDOM_INLINE_HPP

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#include "jfr/utilities/jfrRandom.hpp"

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inline JfrPRNG::JfrPRNG(const void* seed) : _rnd(reinterpret_cast<uint64_t>(seed)) {

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  assert(seed != NULL, "invariant");

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}

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// Returns the next prng value.

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// pRNG is: aX+b mod c with a = 0x5DEECE66D, b =  0xB, c = 1<<48

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// This is the lrand64 generator.

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inline uint64_t next(uint64_t rnd) {

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  static const uint64_t PrngMult = 0x5DEECE66DLL;

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  static const uint64_t PrngAdd = 0xB;

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  static const uint64_t PrngModPower = 48;

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  static const uint64_t PrngModMask = (static_cast<uint64_t>(1) << PrngModPower) - 1;

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  return (PrngMult * rnd + PrngAdd) & PrngModMask;

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}

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inline double JfrPRNG::next_uniform() const {

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  _rnd = next(_rnd);

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  // Take the top 26 bits as the random number

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  // (This plus a 1<<58 sampling bound gives a max possible step of

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  // 5194297183973780480 bytes.  In this case,

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  // for sample_parameter = 1<<19, max possible step is

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  // 9448372 bytes (24 bits).

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  static const uint64_t PrngModPower = 48;  // Number of bits in prng

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  // The uint32_t cast is to prevent a (hard-to-reproduce) NAN

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  // under piii debug for some binaries.

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  // the n_rand value is between 0 and 2**26-1 so it needs to be normalized by dividing by 2**26 (67108864)

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  return (static_cast<uint32_t>(_rnd >> (PrngModPower - 26)) / static_cast<double>(67108864));

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}

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#endif // SHARE_JFR_UTILITIES_JFRRANDOM_INLINE_HPP

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