[patch, libstdc++] std::shuffle: Generate two swap positions at a time if possible

[Eelis van der Weegen]

Ah, thanks, I forgot to re-attach when I sent to include the libstdc++ list.

On 2016-05-03 14:38, Jonathan Wakely wrote:
> ENOPATCH
>
> On 1 May 2016 at 15:21, Eelis <eelis@eelis.net> wrote:
>> Sorry, forgot to include the libstdc++ list.
>>
>> On 2016-05-01 16:18, Eelis wrote:
>>>
>>> Hi,
>>>
>>> The attached patch optimizes std::shuffle for the very common case
>>> where the generator range is large enough that a single invocation
>>> can produce two swap positions.
>>>
>>> This reduces the runtime of the following testcase by 37% on my machine:
>>>
>>>       int main()
>>>       {
>>>           std::mt19937 gen;
>>>
>>>           std::vector<int> v;
>>>           v.reserve(10000);
>>>           for (int i = 0; i != 10000; ++i)
>>>           {
>>>               v.push_back(i);
>>>               std::shuffle(v.begin(), v.end(), gen);
>>>           }
>>>
>>>           std::cout << v.front() << '\n';
>>>       }
>>>
>>> Thoughts?
>>>
>>> Thanks,
>>>
>>> Eelis
>>>
>>
>>

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