58 lines
1.9 KiB
C++
58 lines
1.9 KiB
C++
//===-- RandomNumberGenerator.cpp - Implement RNG class -------------------===//
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//
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// The LLVM Compiler Infrastructure
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//
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// This file is distributed under the University of Illinois Open Source
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// License. See LICENSE.TXT for details.
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//
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//===----------------------------------------------------------------------===//
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//
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// This file implements deterministic random number generation (RNG).
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// The current implementation is NOT cryptographically secure as it uses
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// the C++11 <random> facilities.
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//
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//===----------------------------------------------------------------------===//
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#include "llvm/Support/RandomNumberGenerator.h"
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#include "llvm/Support/CommandLine.h"
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#include "llvm/Support/Debug.h"
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#include "llvm/Support/raw_ostream.h"
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using namespace llvm;
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#define DEBUG_TYPE "rng"
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// Tracking BUG: 19665
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// http://llvm.org/bugs/show_bug.cgi?id=19665
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//
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// Do not change to cl::opt<uint64_t> since this silently breaks argument parsing.
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static cl::opt<unsigned long long>
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Seed("rng-seed", cl::value_desc("seed"),
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cl::desc("Seed for the random number generator"), cl::init(0));
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RandomNumberGenerator::RandomNumberGenerator(StringRef Salt) {
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DEBUG(
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if (Seed == 0)
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dbgs() << "Warning! Using unseeded random number generator.\n"
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);
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// Combine seed and salts using std::seed_seq.
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// Data: Seed-low, Seed-high, Salt
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// Note: std::seed_seq can only store 32-bit values, even though we
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// are using a 64-bit RNG. This isn't a problem since the Mersenne
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// twister constructor copies these correctly into its initial state.
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std::vector<uint32_t> Data;
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Data.reserve(2 + Salt.size());
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Data.push_back(Seed);
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Data.push_back(Seed >> 32);
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std::copy(Salt.begin(), Salt.end(), Data.end());
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std::seed_seq SeedSeq(Data.begin(), Data.end());
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Generator.seed(SeedSeq);
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}
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uint_fast64_t RandomNumberGenerator::operator()() {
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return Generator();
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}
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