copy_if

eve::algo::copy_if = function_with_traits<copy_if_>

inlineconstexpr

#include <eve/module/algo/algo/copy_if.hpp>

Defined in Header

#include <eve/module/algo.hpp>

Note

If you need to apply a transformation, you can use eve::algo::views::map or eve::algo::transform_copy_if.

The main difference from std::copy_if is that it accepts output range and not an output iterator. If the output doesn't have enough space, algorithm will fill all of the avaliable output and then stop. The interface difference allows eve to store more then just selected elements which is important for efficiency.

Note

fix-1656: unfortunately at the moment, we only return where writing output finished. We should return where the input stopped too but we couldn't solve that efficiently so far.

Tuning:

• eve::algo::dense_output/evealgo::sparse_output - if you expect very sparse output (one or two trues per register) - you can pass sparse_output to try to optimize for that.
• Does not support unrolling at the moment. In the exepriments with compress it didn't prove beneficial, but you can always try with eve::algo::for_each, assuming you can overallocate the output.
• Algorithm switches to a much slower version, when there is not enough space to write a full register. Allocating more than input size won't help though.

Callable Signatures

namespace eve::algo
{
   template<relaxed_range In, relaxed_range Out, typename P>
   auto copy_if(In&& in, Out&& out, P p) -> unaligned_iterator_t<Out>
}

** Parameters **

• in - relaxed_range input
• out - relaxed_range output
• p - simd prediocate for elmenets of in

** Return value **

relaxed_iterator past the last written element.

See also

keep_if

remove_if

transform_keep_if

transform_copy_if