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| 1 //===- subzero/src/IceRNG.cpp - PRNG implementation -----------------------===// | 1 //===- subzero/src/IceRNG.cpp - PRNG implementation -----------------------===// |
| 2 // | 2 // |
| 3 // The Subzero Code Generator | 3 // The Subzero Code Generator |
| 4 // | 4 // |
| 5 // This file is distributed under the University of Illinois Open Source | 5 // This file is distributed under the University of Illinois Open Source |
| 6 // License. See LICENSE.TXT for details. | 6 // License. See LICENSE.TXT for details. |
| 7 // | 7 // |
| 8 //===----------------------------------------------------------------------===// | 8 //===----------------------------------------------------------------------===// |
| 9 /// | 9 /// |
| 10 /// \file | 10 /// \file |
| 11 /// This file implements the random number generator. | 11 /// This file implements the random number generator. |
| 12 /// | 12 /// |
| 13 //===----------------------------------------------------------------------===// | 13 //===----------------------------------------------------------------------===// |
| 14 | 14 |
| 15 #include "IceRNG.h" | 15 #include "IceRNG.h" |
| 16 | 16 |
| 17 #include <ctime> | 17 #include <ctime> |
| 18 | 18 |
| 19 namespace Ice { | 19 namespace Ice { |
| 20 | 20 |
| 21 namespace { | 21 namespace { |
| 22 constexpr unsigned MAX = 2147483647; | 22 constexpr unsigned MAX = 2147483647; |
| 23 } // end of anonymous namespace | 23 } // end of anonymous namespace |
| 24 | 24 |
| 25 // TODO(wala,stichnot): Switch to RNG implementation from LLVM or C++11. | 25 // TODO(wala,stichnot): Switch to RNG implementation from LLVM or C++11. |
| 26 // | 26 // |
| 27 // TODO(wala,stichnot): Make it possible to replay the RNG sequence in a | 27 // TODO(wala,stichnot): Make it possible to replay the RNG sequence in a |
| 28 // subsequent run, for reproducing a bug. Print the seed in a comment | 28 // subsequent run, for reproducing a bug. Print the seed in a comment in the |
| 29 // in the asm output. Embed the seed in the binary via metadata that an | 29 // asm output. Embed the seed in the binary via metadata that an attacker can't |
| 30 // attacker can't introspect. | 30 // introspect. |
| 31 RandomNumberGenerator::RandomNumberGenerator(uint64_t Seed, llvm::StringRef) | 31 RandomNumberGenerator::RandomNumberGenerator(uint64_t Seed, llvm::StringRef) |
| 32 : State(Seed) {} | 32 : State(Seed) {} |
| 33 | 33 |
| 34 RandomNumberGenerator::RandomNumberGenerator( | 34 RandomNumberGenerator::RandomNumberGenerator( |
| 35 uint64_t Seed, RandomizationPassesEnum RandomizationPassID, uint64_t Salt) { | 35 uint64_t Seed, RandomizationPassesEnum RandomizationPassID, uint64_t Salt) { |
| 36 constexpr unsigned NumBitsGlobalSeed = CHAR_BIT * sizeof(State); | 36 constexpr unsigned NumBitsGlobalSeed = CHAR_BIT * sizeof(State); |
| 37 constexpr unsigned NumBitsPassID = 4; | 37 constexpr unsigned NumBitsPassID = 4; |
| 38 constexpr unsigned NumBitsSalt = 12; | 38 constexpr unsigned NumBitsSalt = 12; |
| 39 static_assert(RPE_num < (1 << NumBitsPassID), "NumBitsPassID too small"); | 39 static_assert(RPE_num < (1 << NumBitsPassID), "NumBitsPassID too small"); |
| 40 State = Seed ^ ((uint64_t)RandomizationPassID | 40 State = Seed ^ ((uint64_t)RandomizationPassID |
| 41 << (NumBitsGlobalSeed - NumBitsPassID)) ^ | 41 << (NumBitsGlobalSeed - NumBitsPassID)) ^ |
| 42 (Salt << (NumBitsGlobalSeed - NumBitsPassID - NumBitsSalt)); | 42 (Salt << (NumBitsGlobalSeed - NumBitsPassID - NumBitsSalt)); |
| 43 } | 43 } |
| 44 uint64_t RandomNumberGenerator::next(uint64_t Max) { | 44 uint64_t RandomNumberGenerator::next(uint64_t Max) { |
| 45 // Lewis, Goodman, and Miller (1969) | 45 // Lewis, Goodman, and Miller (1969) |
| 46 State = (16807 * State) % MAX; | 46 State = (16807 * State) % MAX; |
| 47 return State % Max; | 47 return State % Max; |
| 48 } | 48 } |
| 49 | 49 |
| 50 bool RandomNumberGeneratorWrapper::getTrueWithProbability(float Probability) { | 50 bool RandomNumberGeneratorWrapper::getTrueWithProbability(float Probability) { |
| 51 return RNG.next(MAX) < Probability * MAX; | 51 return RNG.next(MAX) < Probability * MAX; |
| 52 } | 52 } |
| 53 | 53 |
| 54 } // end of namespace Ice | 54 } // end of namespace Ice |
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