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Random Number Generator (llvm)

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Summary:
Provides an abstraction for a random number generator (RNG) that produces a stream of pseudo-random numbers.
The current implementation uses C++11 facilities and is therefore not cryptographically secure.

The RNG is salted with the text of the current command line invocation.
In addition, a user may specify a seed (reproducible builds).

In clang, the seed can be set via
  -frandom-seed=X
In the back end, the seed can be set via
  -rng-seed=X

This is the llvm part of the patch.
clang part: D3391

Reviewers: ahomescu, rinon, nicholas, jfb

Reviewed By: jfb

Subscribers: jfb, perl

Differential Revision: http://reviews.llvm.org/D3390

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@211145 91177308-0d34-0410-b5e6-96231b3b80d8
This commit is contained in:
JF Bastien
2014-06-18 06:23:25 +00:00
parent 74287ec34c
commit 1d04a2324c
5 changed files with 128 additions and 1 deletions
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52
lib/Support/RandomNumberGenerator.cpp Normal file
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//===-- RandomNumberGenerator.cpp - Implement RNG class -------------------===//
//
// The LLVM Compiler Infrastructure
//
// This file is distributed under the University of Illinois Open Source
// License. See LICENSE.TXT for details.
//
//===----------------------------------------------------------------------===//
//
// This file implements random number generation (RNG).
// The current implementation is NOT cryptographically secure as it uses
// the C++11 <random> facilities.
//
//===----------------------------------------------------------------------===//
#define DEBUG_TYPE "rng"
#include "llvm/Support/RandomNumberGenerator.h"
#include "llvm/Support/CommandLine.h"
#include "llvm/Support/Debug.h"
using namespace llvm;
// Tracking BUG: 19665
// http://llvm.org/bugs/show_bug.cgi?id=19665
//
// Do not change to cl::opt<uint64_t> since this silently breaks argument parsing.
static cl::opt<unsigned long long>
Seed("rng-seed", cl::value_desc("seed"),
cl::desc("Seed for the random number generator"), cl::init(0));
RandomNumberGenerator::RandomNumberGenerator(StringRef Salt) {
DEBUG(
if (Seed == 0)
errs() << "Warning! Using unseeded random number generator.\n"
);
// Combine seed and salt using std::seed_seq.
// Entropy: Seed-low, Seed-high, Salt...
size_t Size = Salt.size() + 2;
uint32_t Data[Size];
Data[0] = Seed;
Data[1] = Seed >> 32;
std::copy_n(Salt.begin(), Salt.size(), Data + 2);
std::seed_seq SeedSeq(Data, Data + Size);
Generator.seed(SeedSeq);
}
uint64_t RandomNumberGenerator::next(uint64_t Max) {
std::uniform_int_distribution<uint64_t> distribution(0, Max - 1);
return distribution(Generator);
}