随机数，C ++ 11 vs Boost [英] Random numbers, C++11 vs Boost

问题描述

我想在C ++中生成伪随机数，这两个可能的选项是C ++ 11和Boost对应项的功能.它们的使用方式基本上相同，但是在我的测试中，原生速度大约慢了4倍.

I want to generate pseudo-random numbers in C++, and the two likely options are the feature of C++11 and the Boost counterpart. They are used in essentially the same way, but the native one in my tests is roughly 4 times slower.

是由于库中的设计选择，还是我缺少某种在某处禁用调试代码的方式?

Is that due to design choices in the library, or am I missing some way of disabling debug code somewhere?

更新:代码在此处， https ://github.com/vbeffara/Simulations/blob/master/tests/test_prng.cpp 看起来像这样:

Update: Code is here, https://github.com/vbeffara/Simulations/blob/master/tests/test_prng.cpp and looks like this:

cerr << "boost::bernoulli_distribution ...      \ttime = ";
s=0; t=time();
boost::bernoulli_distribution<> dist(.5);
boost::mt19937 boostengine;
for (int i=0; i<n; ++i) s += dist(boostengine);
cerr << time()-t << ",  \tsum = " << s << endl;

cerr << "C++11 style ...                        \ttime = ";
s=0; t=time();
std::bernoulli_distribution dist2(.5);
std::mt19937_64 engine;
for (int i=0; i<n; ++i) s += dist2(engine);
cerr << time()-t << ",  \tsum = " << s << endl;

(使用std::mt19937而不是std::mt19937_64会使它在我的系统上更慢.)

(Using std::mt19937 instead of std::mt19937_64 makes it even slower on my system.)

推荐答案

那很漂亮可怕的.

让我们看看:

boost :: bernoulli_distribution<>

boost::bernoulli_distribution<>

if(_p == RealType(0))
    return false;
else
    return RealType(eng()-(eng.min)()) <= _p * RealType((eng.max)()-(eng.min)());

std :: bernoulli_distribution

std::bernoulli_distribution

__detail::_Adaptor<_UniformRandomNumberGenerator, double> __aurng(__urng);
if ((__aurng() - __aurng.min()) < __p.p() * (__aurng.max() - __aurng.min()))
    return true;
return false;

两个版本都调用引擎，并检查输出是否在与给定概率成比例的值范围内.

Both versions invoke the engine and check if the output lies in a portion of the range of values proportional to the given probability.

最大的区别在于，gcc版本调用了助手类_Adaptor的函数.

The big difference is, that the gcc version calls the functions of a helper class _Adaptor.

此类的min和max函数分别返回0和1，然后operator()然后使用给定的URNG调用std::generate_canonical以获取介于0和1之间的值.

This class’ min and max functions return 0 and 1 respectively and operator() then calls std::generate_canonical with the given URNG to obtain a value between 0 and 1.

std::generate_canonical是带有循环的20行函数–在这种情况下，它永远不会重复多次，但会增加复杂性.

std::generate_canonical is a 20 line function with a loop – which will never iteratate more than once in this case, but it adds complexity.

除此之外，boost仅在发行版的构造函数中使用param_type，然后将_p保存为double成员，而gcc具有param_type成员，并且必须获取"值它的.

Apart from that, boost uses the param_type only in the constructor of the distribution, but then saves _p as a double member, whereas gcc has a param_type member and has to "get" the value of it.

这一切融合在一起，编译器无法进行优化. 铛声在它上面窒息了更多.

This all comes together and the compiler fails in optimizing. Clang chokes even more on it.

如果您锤子足够硬，您甚至可以获得std::mt19937和boost::mt19937 en等于gcc.

If you hammer hard enough you can even get std::mt19937 and boost::mt19937 en par for gcc.

也可以测试libc ++，也许以后再补充.

It would be nice to test libc++ too, maybe i’ll add that later.

经过测试的版本:boost 1.55.0，gcc 4.8.2的libstdc ++标头
根据要求提供行号^^

tested versions: boost 1.55.0, libstdc++ headers of gcc 4.8.2
line numbers on request^^

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