LLVM  3.7.0
RandomNumberGenerator.cpp
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1 //===-- RandomNumberGenerator.cpp - Implement RNG class -------------------===//
2 //
3 // The LLVM Compiler Infrastructure
4 //
5 // This file is distributed under the University of Illinois Open Source
6 // License. See LICENSE.TXT for details.
7 //
8 //===----------------------------------------------------------------------===//
9 //
10 // This file implements deterministic random number generation (RNG).
11 // The current implementation is NOT cryptographically secure as it uses
12 // the C++11 <random> facilities.
13 //
14 //===----------------------------------------------------------------------===//
15 
18 #include "llvm/Support/Debug.h"
20 
21 using namespace llvm;
22 
23 #define DEBUG_TYPE "rng"
24 
25 // Tracking BUG: 19665
26 // http://llvm.org/bugs/show_bug.cgi?id=19665
27 //
28 // Do not change to cl::opt<uint64_t> since this silently breaks argument parsing.
30 Seed("rng-seed", cl::value_desc("seed"),
31  cl::desc("Seed for the random number generator"), cl::init(0));
32 
33 RandomNumberGenerator::RandomNumberGenerator(StringRef Salt) {
34  DEBUG(
35  if (Seed == 0)
36  dbgs() << "Warning! Using unseeded random number generator.\n"
37  );
38 
39  // Combine seed and salts using std::seed_seq.
40  // Data: Seed-low, Seed-high, Salt
41  // Note: std::seed_seq can only store 32-bit values, even though we
42  // are using a 64-bit RNG. This isn't a problem since the Mersenne
43  // twister constructor copies these correctly into its initial state.
44  std::vector<uint32_t> Data;
45  Data.reserve(2 + Salt.size());
46  Data.push_back(Seed);
47  Data.push_back(Seed >> 32);
48 
49  std::copy(Salt.begin(), Salt.end(), Data.end());
50 
51  std::seed_seq SeedSeq(Data.begin(), Data.end());
52  Generator.seed(SeedSeq);
53 }
54 
56  return Generator();
57 }
static cl::opt< unsigned long long > Seed("rng-seed", cl::value_desc("seed"), cl::desc("Seed for the random number generator"), cl::init(0))
size_t size() const
size - Get the string size.
Definition: StringRef.h:113
uint_fast64_t operator()()
Returns a random number in the range [0, Max).
iterator begin() const
Definition: StringRef.h:90
initializer< Ty > init(const Ty &Val)
Definition: CommandLine.h:325
raw_ostream & dbgs()
dbgs() - This returns a reference to a raw_ostream for debugging messages.
Definition: Debug.cpp:123
iterator end() const
Definition: StringRef.h:92
#define DEBUG(X)
Definition: Debug.h:92
StringRef - Represent a constant reference to a string, i.e.
Definition: StringRef.h:40