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//===- subzero/src/IceRNG.cpp - PRNG implementation -----------------------===//
//
// The Subzero Code Generator
//
// This file is distributed under the University of Illinois Open Source
// License. See LICENSE.TXT for details.
//
//===----------------------------------------------------------------------===//
///
/// \file
/// \brief Implements the random number generator.
///
//===----------------------------------------------------------------------===//
#include "IceRNG.h"
#include <climits>
#include <ctime>
namespace Ice {
namespace {
constexpr unsigned MAX = 2147483647;
} // end of anonymous namespace
// TODO(wala,stichnot): Switch to RNG implementation from LLVM or C++11.
//
// TODO(wala,stichnot): Make it possible to replay the RNG sequence in a
// subsequent run, for reproducing a bug. Print the seed in a comment in the
// asm output. Embed the seed in the binary via metadata that an attacker can't
// introspect.
RandomNumberGenerator::RandomNumberGenerator(uint64_t Seed, llvm::StringRef)
: State(Seed) {}
RandomNumberGenerator::RandomNumberGenerator(
uint64_t Seed, RandomizationPassesEnum RandomizationPassID, uint64_t Salt) {
constexpr unsigned NumBitsGlobalSeed = CHAR_BIT * sizeof(State);
constexpr unsigned NumBitsPassID = 4;
constexpr unsigned NumBitsSalt = 12;
static_assert(RPE_num < (1 << NumBitsPassID), "NumBitsPassID too small");
State =
Seed ^
((uint64_t)RandomizationPassID << (NumBitsGlobalSeed - NumBitsPassID)) ^
(Salt << (NumBitsGlobalSeed - NumBitsPassID - NumBitsSalt));
}
uint64_t RandomNumberGenerator::next(uint64_t Max) {
// Lewis, Goodman, and Miller (1969)
State = (16807 * State) % MAX;
return State % Max;
}
bool RandomNumberGeneratorWrapper::getTrueWithProbability(float Probability) {
return static_cast<float>(RNG.next(MAX)) < Probability * static_cast<float>(MAX);
}
} // end of namespace Ice
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