[Patch] Optimize _BFSExecutor in regex

[Tim Shen]

On Mon, Oct 7, 2013 at 1:28 PM, Jonathan Wakely <jwakely.gcc@gmail.com> wrote:
> std::memset() on about 125 bytes is not a big deal, I doubt it's
> significantly more expensive than the calculations to find the right
> bits and do the necessary masking for three elements.
> std::vector<bool> is a strange beast, remember.

OK so I may change to use something else(bitset?) next time I encounter this.

Is copying 125 bytes more expensive comparing to 3 assignment and
substrction? Because it *is* cheap to find all elements that's true,
they are just in _M_base(in the latest patch). So:

while (!this->empty())
    this->pop();

...will be executed only 3 times. I think it's cheaper than copying a
long-enough and sparse-enough byte chunk? Or at least we should theck
the density(_M_base.size() / _M_exists.size()) of _M_exists ?


-- 
Tim Shen