```//////////////////////////////////////////////////////////////////////////////
//
// (C) Copyright Ion Gaztanaga 2015-2016.
// (See accompanying file LICENSE_1_0.txt or copy at
//
// See http://www.boost.org/libs/move for documentation.
//
//////////////////////////////////////////////////////////////////////////////
//
// Stable sorting that works in O(N*log(N)) worst time
// and uses O(1) extra memory
//
//////////////////////////////////////////////////////////////////////////////
//
// The main idea of the adaptive_sort algorithm was developed by Andrey Astrelin
// and explained in the article from the russian collaborative blog
// Habrahabr (http://habrahabr.ru/post/205290/). The algorithm is based on
// ideas from B-C. Huang and M. A. Langston explained in their article
// "Fast Stable Merging and Sorting in Constant Extra Space (1989-1992)"
// (http://comjnl.oxfordjournals.org/content/35/6/643.full.pdf).
//
// This implementation by Ion Gaztanaga uses previous ideas with additional changes:
//
// - Use of GCD-based rotation.
// - Non power of two buffer-sizes.
// - Tries to find sqrt(len)*2 unique keys, so that the merge sort
//   phase can form up to sqrt(len)*4 segments if enough keys are found.
// - The merge-sort phase can take advantage of external memory to
//   save some additional combination steps.
// - Combination phase: Blocks are selection sorted and merged in parallel.
// - The combination phase is performed alternating merge to left and merge
//   to right phases minimizing swaps due to internal buffer repositioning.
// - When merging blocks special optimizations are made to avoid moving some
//   elements twice.
//
// The adaptive_merge algorithm was developed by Ion Gaztanaga reusing some parts
// from the sorting algorithm and implementing an additional block merge algorithm
// without moving elements to left or right.
//////////////////////////////////////////////////////////////////////////////

#include <boost/move/detail/config_begin.hpp>
#include <boost/move/detail/reverse_iterator.hpp>
#include <boost/move/algo/move.hpp>
#include <boost/move/algo/detail/merge.hpp>
#include <boost/move/algo/detail/insertion_sort.hpp>
#include <boost/move/algo/detail/merge_sort.hpp>
#include <boost/move/algo/detail/heap_sort.hpp>
#include <boost/move/algo/detail/merge.hpp>
#include <boost/move/algo/detail/is_sorted.hpp>
#include <boost/core/ignore_unused.hpp>
#include <boost/assert.hpp>
#include <boost/cstdint.hpp>

#endif

print_stats(STR, L)\
//

print_stats(STR, L)\
//
#else
print_stats(STR, L)\
//

#endif
#else
#endif

#else
#endif

namespace boost {
namespace movelib {

bool is_sorted(::order_perf_type *first, ::order_perf_type *last, ::order_type_less)
{
if (first != last) {
const order_perf_type *next = first, *cur(first);
while (++next != last) {
if (!(cur->key < next->key || (cur->key == next->key && cur->val < next->val)))
return false;
cur = next;
}
}
return true;
}

static const std::size_t AdaptiveSortInsertionSortThreshold = 16;
//static const std::size_t AdaptiveSortInsertionSortThreshold = 4;

#if defined BOOST_HAS_INTPTR_T
typedef ::boost::uintptr_t uintptr_t;
#else
typedef std::size_t uintptr_t;
#endif

template<class T>
const T &min_value(const T &a, const T &b)
{
return a < b ? a : b;
}

template<class T>
const T &max_value(const T &a, const T &b)
{
return a > b ? a : b;
}

template<class ForwardIt, class Pred, class V>
typename iterator_traits<ForwardIt>::size_type
count_if_with(ForwardIt first, ForwardIt last, Pred pred, const V &v)
{
typedef typename iterator_traits<ForwardIt>::size_type size_type;
size_type count = 0;
while(first != last) {
count += static_cast<size_type>(0 != pred(*first, v));
++first;
}
return count;
}

template<class RandIt, class Compare>
RandIt skip_until_merge
( RandIt first1, RandIt const last1
, const typename iterator_traits<RandIt>::value_type &next_key, Compare comp)
{
while(first1 != last1 && !comp(next_key, *first1)){
++first1;
}
return first1;
}

template<class RandItKeys, class RandIt>
void swap_and_update_key
( RandItKeys const key_next
, RandItKeys const key_range2
, RandItKeys &key_mid
, RandIt const begin
, RandIt const end
, RandIt const with)
{
if(begin != with){
if(key_next == key_mid){
key_mid = key_range2;
}
else if(key_mid == key_range2){
key_mid = key_next;
}
}
}

template<class RandItKeys>
void update_key
(RandItKeys const key_next
, RandItKeys const key_range2
, RandItKeys &key_mid)
{
if (key_next != key_range2) {
if (key_next == key_mid) {
key_mid = key_range2;
}
else if (key_mid == key_range2) {
key_mid = key_next;
}
}
}

template<class RandItKeys, class RandIt, class RandIt2, class Op>
RandIt2 buffer_and_update_key
(RandItKeys const key_next
, RandItKeys const key_range2
, RandItKeys &key_mid
, RandIt begin
, RandIt end
, RandIt with
, RandIt2 buffer
, Op op)
{
if (begin != with) {
while(begin != end) {
op(three_way_t(), begin++, with++, buffer++);
}
if (key_next == key_mid) {
key_mid = key_range2;
}
else if (key_mid == key_range2) {
key_mid = key_next;
}
}
return buffer;
}

///////////////////////////////////////////////////////////////////////////////
//
//                         MERGE BUFFERLESS
//
///////////////////////////////////////////////////////////////////////////////

// [first1, last1) merge [last1,last2) -> [first1,last2)
template<class RandIt, class Compare>
RandIt partial_merge_bufferless_impl
(RandIt first1, RandIt last1, RandIt const last2, bool *const pis_range1_A, Compare comp)
{
if(last1 == last2){
return first1;
}
bool const is_range1_A = *pis_range1_A;
if(first1 != last1 && comp(*last1, last1[-1])){
do{
RandIt const old_last1 = last1;
last1  = boost::movelib::lower_bound(last1, last2, *first1, comp);
first1 = rotate_gcd(first1, old_last1, last1);//old_last1 == last1 supported
if(last1 == last2){
return first1;
}
do{
++first1;
} while(last1 != first1 && !comp(*last1, *first1) );
} while(first1 != last1);
}
*pis_range1_A = !is_range1_A;
return last1;
}

// [first1, last1) merge [last1,last2) -> [first1,last2)
template<class RandIt, class Compare>
RandIt partial_merge_bufferless
(RandIt first1, RandIt last1, RandIt const last2, bool *const pis_range1_A, Compare comp)
{
return *pis_range1_A ? partial_merge_bufferless_impl(first1, last1, last2, pis_range1_A, comp)
: partial_merge_bufferless_impl(first1, last1, last2, pis_range1_A, antistable<Compare>(comp));
}

template<class SizeType>
static SizeType needed_keys_count(SizeType n_block_a, SizeType n_block_b)
{
return n_block_a + n_block_b;
}

template<class RandItKeys, class KeyCompare, class RandIt, class Compare>
typename iterator_traits<RandIt>::size_type
find_next_block
( RandItKeys const key_first
, KeyCompare key_comp
, RandIt const first
, typename iterator_traits<RandIt>::size_type const l_block
, typename iterator_traits<RandIt>::size_type const ix_first_block
, typename iterator_traits<RandIt>::size_type const ix_last_block
, Compare comp)
{
typedef typename iterator_traits<RandIt>::size_type      size_type;
typedef typename iterator_traits<RandIt>::value_type     value_type;
typedef typename iterator_traits<RandItKeys>::value_type key_type;
BOOST_ASSERT(ix_first_block <= ix_last_block);
size_type ix_min_block = 0u;
for (size_type szt_i = ix_first_block; szt_i < ix_last_block; ++szt_i) {
const value_type &min_val = first[ix_min_block*l_block];
const value_type &cur_val = first[szt_i*l_block];
const key_type   &min_key = key_first[ix_min_block];
const key_type   &cur_key = key_first[szt_i];

bool const less_than_minimum = comp(cur_val, min_val) ||
(!comp(min_val, cur_val) && key_comp(cur_key, min_key));

if (less_than_minimum) {
ix_min_block = szt_i;
}
}
return ix_min_block;
}

template<class RandItKeys, class KeyCompare, class RandIt, class Compare>
void merge_blocks_bufferless
( RandItKeys const key_first
, KeyCompare key_comp
, RandIt const first
, typename iterator_traits<RandIt>::size_type const l_block
, typename iterator_traits<RandIt>::size_type const l_irreg1
, typename iterator_traits<RandIt>::size_type const n_block_a
, typename iterator_traits<RandIt>::size_type const n_block_b
, typename iterator_traits<RandIt>::size_type const l_irreg2
, Compare comp)
{
typedef typename iterator_traits<RandIt>::size_type size_type;
size_type const key_count = needed_keys_count(n_block_a, n_block_b);
::boost::ignore_unused(key_count);
//BOOST_ASSERT(n_block_a || n_block_b);
BOOST_MOVE_ADAPTIVE_SORT_INVARIANT(!n_block_b || n_block_a == count_if_with(key_first, key_first + key_count, key_comp, key_first[n_block_a]));

size_type n_bef_irreg2 = 0;
bool l_irreg_pos_count = true;
RandItKeys key_mid(key_first + n_block_a);
RandIt const first_irr2 = first + l_irreg1 + (n_block_a+n_block_b)*l_block;
RandIt const last_irr2  = first_irr2 + l_irreg2;

{  //Selection sort blocks
size_type n_block_left = n_block_b + n_block_a;
RandItKeys key_range2(key_first);

size_type min_check = n_block_a == n_block_left ? 0u : n_block_a;
size_type max_check = min_value<size_type>(min_check+1, n_block_left);
for (RandIt f = first+l_irreg1; n_block_left; --n_block_left, ++key_range2, f += l_block, min_check -= min_check != 0, max_check -= max_check != 0) {
size_type const next_key_idx = find_next_block(key_range2, key_comp, f, l_block, min_check, max_check, comp);
RandItKeys const key_next(key_range2 + next_key_idx);
max_check = min_value<size_type>(max_value<size_type>(max_check, next_key_idx+size_type(2)), n_block_left);

RandIt const first_min = f + next_key_idx*l_block;

//Check if irregular b block should go here.
//If so, break to the special code handling the irregular block
if (l_irreg_pos_count && l_irreg2 && comp(*first_irr2, *first_min)){
l_irreg_pos_count = false;
}
n_bef_irreg2 += l_irreg_pos_count;

swap_and_update_key(key_next, key_range2, key_mid, f, f + l_block, first_min);
BOOST_MOVE_ADAPTIVE_SORT_INVARIANT((f == (first+l_irreg1)) || !comp(*f, *(f-l_block)));
}
}

RandIt first1 = first;
RandIt last1  = first+l_irreg1;
RandItKeys const key_end (key_first+n_bef_irreg2);
bool is_range1_A = true;

for(RandItKeys key_next = key_first; key_next != key_end; ++key_next){
bool is_range2_A = key_mid == (key_first+key_count) || key_comp(*key_next, *key_mid);
first1 = is_range1_A == is_range2_A
? last1 : partial_merge_bufferless(first1, last1, last1 + l_block, &is_range1_A, comp);
last1 += l_block;
}

merge_bufferless(is_range1_A ? first1 : last1, first_irr2, last_irr2, comp);
}

// Complexity: 2*distance(first, last)+max_collected^2/2
//
// Tries to collect at most n_keys unique elements from [first, last),
// in the begining of the range, and ordered according to comp
//
// Returns the number of collected keys
template<class RandIt, class Compare, class XBuf>
typename iterator_traits<RandIt>::size_type
collect_unique
( RandIt const first, RandIt const last
, typename iterator_traits<RandIt>::size_type const max_collected, Compare comp
, XBuf & xbuf)
{
typedef typename iterator_traits<RandIt>::size_type size_type;
size_type h = 0;
if(max_collected){
++h;  // first key is always here
RandIt h0 = first;
RandIt u = first; ++u;
RandIt search_end = u;

if(xbuf.capacity() >= max_collected){
typename XBuf::iterator const ph0 = xbuf.add(first);
while(u != last && h < max_collected){
typename XBuf::iterator const r = boost::movelib::lower_bound(ph0, xbuf.end(), *u, comp);
if(r == xbuf.end() || comp(*u, *r) ){
RandIt const new_h0 = boost::move(search_end, u, h0);
search_end = u;
++search_end;
++h;
xbuf.insert(r, u);
h0 = new_h0;
}
++u;
}
boost::move_backward(first, h0, h0+h);
boost::move(xbuf.data(), xbuf.end(), first);
}
else{
while(u != last && h < max_collected){
RandIt const r = boost::movelib::lower_bound(h0, search_end, *u, comp);
if(r == search_end || comp(*u, *r) ){
RandIt const new_h0 = rotate_gcd(h0, search_end, u);
search_end = u;
++search_end;
++h;
rotate_gcd(r+(new_h0-h0), u, search_end);
h0 = new_h0;
}
++u;
}
rotate_gcd(first, h0, h0+h);
}
}
return h;
}

template<class Unsigned>
Unsigned floor_sqrt(Unsigned const n)
{
Unsigned x = n;
Unsigned y = x/2 + (x&1);
while (y < x){
x = y;
y = (x + n / x)/2;
}
return x;
}

template<class Unsigned>
Unsigned ceil_sqrt(Unsigned const n)
{
Unsigned r = floor_sqrt(n);
return r + Unsigned((n%r) != 0);
}

template<class Unsigned>
Unsigned floor_merge_multiple(Unsigned const n, Unsigned &base, Unsigned &pow)
{
Unsigned s = n;
Unsigned p = 0;
s /= 2;
++p;
}
base = s;
pow = p;
return s << p;
}

template<class Unsigned>
Unsigned ceil_merge_multiple(Unsigned const n, Unsigned &base, Unsigned &pow)
{
Unsigned fm = floor_merge_multiple(n, base, pow);

if(fm != n){
++base;
}
else{
++pow;
}
}
return base << pow;
}

template<class Unsigned>
Unsigned ceil_sqrt_multiple(Unsigned const n, Unsigned *pbase = 0)
{
Unsigned const r = ceil_sqrt(n);
Unsigned pow = 0;
Unsigned base = 0;
Unsigned const res = ceil_merge_multiple(r, base, pow);
if(pbase) *pbase = base;
return res;
}

struct less
{
template<class T>
bool operator()(const T &l, const T &r)
{  return l < r;  }
};

///////////////////////////////////////////////////////////////////////////////
//
//                            MERGE BLOCKS
//
///////////////////////////////////////////////////////////////////////////////

template<class RandIt, class Compare>
void slow_stable_sort
( RandIt const first, RandIt const last, Compare comp)
{
boost::movelib::inplace_stable_sort(first, last, comp);
}

template<class RandIt, class Compare>
void slow_stable_sort
( RandIt const first, RandIt const last, Compare comp)
{
typedef typename iterator_traits<RandIt>::size_type size_type;
size_type L = size_type(last - first);
{  //Use insertion sort to merge first elements
size_type m = 0;
}
insertion_sort(first+m, last, comp);
}

for(bool do_merge = L > h; do_merge; h*=2){
do_merge = (L - h) > h;
size_type p0 = 0;
if(do_merge){
size_type const h_2 = 2*h;
while((L-p0) > h_2){
merge_bufferless(first+p0, first+p0+h, first+p0+h_2, comp);
p0 += h_2;
}
}
if((L-p0) > h){
merge_bufferless(first+p0, first+p0+h, last, comp);
}
}
}

//Returns new l_block and updates use_buf
template<class Unsigned>
Unsigned lblock_for_combine
(Unsigned const l_block, Unsigned const n_keys, Unsigned const l_data, bool &use_buf)
{
BOOST_ASSERT(l_data > 1);

//We need to guarantee lblock >= l_merged/(n_keys/2) keys for the combination.
//We have at least 4 keys guaranteed (which are the minimum to merge 2 ranges)
//If l_block != 0, then n_keys is already enough to merge all blocks in all
//phases as we've found all needed keys for that buffer and length before.
//If l_block == 0 then see if half keys can be used as buffer and the rest
//as keys guaranteeing that n_keys >= (2*l_merged)/lblock =
if(!l_block){
//If l_block == 0 then n_keys is power of two
//(guaranteed by build_params(...))
BOOST_ASSERT(n_keys >= 4);
//BOOST_ASSERT(0 == (n_keys &(n_keys-1)));

//See if half keys are at least 4 and if half keys fulfill
Unsigned const new_buf  = n_keys/2;
Unsigned const new_keys = n_keys-new_buf;
use_buf = new_keys >= 4 && new_keys >= l_data/new_buf;
if(use_buf){
return new_buf;
}
else{
return l_data/n_keys;
}
}
else{
use_buf = true;
return l_block;
}
}

template<class RandIt, class Compare, class XBuf>
void stable_sort( RandIt first, RandIt last, Compare comp, XBuf & xbuf)
{
typedef typename iterator_traits<RandIt>::size_type size_type;
size_type const len = size_type(last - first);
size_type const half_len = len/2 + (len&1);
if(std::size_t(xbuf.capacity() - xbuf.size()) >= half_len) {
merge_sort(first, last, comp, xbuf.data()+xbuf.size());
}
else{
slow_stable_sort(first, last, comp);
}
}

template<class RandIt, class Comp, class XBuf>
void unstable_sort( RandIt first, RandIt last
, Comp comp
, XBuf & xbuf)
{
heap_sort(first, last, comp);
::boost::ignore_unused(xbuf);
}

template<class RandIt, class Compare, class XBuf>
void stable_merge
( RandIt first, RandIt const middle, RandIt last
, Compare comp
, XBuf &xbuf)
{
BOOST_ASSERT(xbuf.empty());
typedef typename iterator_traits<RandIt>::size_type   size_type;
size_type const len1  = size_type(middle-first);
size_type const len2  = size_type(last-middle);
size_type const l_min = min_value<size_type>(len1, len2);
if(xbuf.capacity() >= l_min){
buffered_merge(first, middle, last, comp, xbuf);
xbuf.clear();
}
else{
//merge_bufferless(first, middle, last, comp);
merge_adaptive_ONlogN(first, middle, last, comp, xbuf.begin(), xbuf.capacity());
}
}

template<class RandIt, class Comp, class XBuf>
void initialize_keys( RandIt first, RandIt last
, Comp comp
, XBuf & xbuf)
{
unstable_sort(first, last, comp, xbuf);
BOOST_ASSERT(boost::movelib::is_sorted_and_unique(first, last, comp));
}

template<class RandIt, class U>
void initialize_keys( RandIt first, RandIt last
, less
, U &)
{
typedef typename iterator_traits<RandIt>::value_type value_type;
std::size_t count = std::size_t(last - first);
for(std::size_t i = 0; i != count; ++i){
*first = static_cast<value_type>(i);
++first;
}
}

template <class Unsigned>
Unsigned calculate_total_combined(Unsigned const len, Unsigned const l_prev_merged, Unsigned *pl_irreg_combined = 0)
{
typedef Unsigned size_type;

size_type const l_combined = 2*l_prev_merged;
size_type l_irreg_combined = len%l_combined;
size_type l_total_combined = len;
if(l_irreg_combined <= l_prev_merged){
l_total_combined -= l_irreg_combined;
l_irreg_combined = 0;
}
if(pl_irreg_combined)
*pl_irreg_combined = l_irreg_combined;
return l_total_combined;
}

template<class RandItKeys, class KeyCompare, class SizeType, class XBuf>
void combine_params
( RandItKeys const keys
, KeyCompare key_comp
, SizeType l_combined
, SizeType const l_prev_merged
, SizeType const l_block
, XBuf & xbuf
//Output
, SizeType &n_block_a
, SizeType &n_block_b
, SizeType &l_irreg1
, SizeType &l_irreg2
//Options
, bool do_initialize_keys = true)
{
typedef SizeType   size_type;

//Initial parameters for selection sort blocks
l_irreg1 = l_prev_merged%l_block;
l_irreg2 = (l_combined-l_irreg1)%l_block;
BOOST_ASSERT(((l_combined-l_irreg1-l_irreg2)%l_block) == 0);
size_type const n_reg_block = (l_combined-l_irreg1-l_irreg2)/l_block;
n_block_a = l_prev_merged/l_block;
n_block_b = n_reg_block - n_block_a;
BOOST_ASSERT(n_reg_block>=n_block_a);

//Key initialization
if (do_initialize_keys) {
initialize_keys(keys, keys + needed_keys_count(n_block_a, n_block_b), key_comp, xbuf);
}
}

//////////////////////////////////
//
//          partial_merge
//
//////////////////////////////////
template<class InputIt1, class InputIt2, class OutputIt, class Compare, class Op>
OutputIt op_partial_merge_impl
(InputIt1 &r_first1, InputIt1 const last1, InputIt2 &r_first2, InputIt2 const last2, OutputIt d_first, Compare comp, Op op)
{
InputIt1 first1(r_first1);
InputIt2 first2(r_first2);
if(first2 != last2 && last1 != first1)
while(1){
if(comp(*first2, *first1)) {
op(first2++, d_first++);
if(first2 == last2){
break;
}
}
else{
op(first1++, d_first++);
if(first1 == last1){
break;
}
}
}
r_first1 = first1;
r_first2 = first2;
return d_first;
}

template<class InputIt1, class InputIt2, class OutputIt, class Compare, class Op>
OutputIt op_partial_merge
(InputIt1 &r_first1, InputIt1 const last1, InputIt2 &r_first2, InputIt2 const last2, OutputIt d_first, Compare comp, Op op, bool is_stable)
{
return is_stable ? op_partial_merge_impl(r_first1, last1, r_first2, last2, d_first, comp, op)
: op_partial_merge_impl(r_first1, last1, r_first2, last2, d_first, antistable<Compare>(comp), op);
}

//////////////////////////////////
//////////////////////////////////
//////////////////////////////////
//
//    op_partial_merge_and_save
//
//////////////////////////////////
//////////////////////////////////
//////////////////////////////////
template<class InputIt1, class InputIt2, class OutputIt, class Compare, class Op>
OutputIt op_partial_merge_and_swap_impl
(InputIt1 &r_first1, InputIt1 const last1, InputIt2 &r_first2, InputIt2 const last2, InputIt2 &r_first_min, OutputIt d_first, Compare comp, Op op)
{
InputIt1 first1(r_first1);
InputIt2 first2(r_first2);

if(first2 != last2 && last1 != first1) {
InputIt2 first_min(r_first_min);
bool non_empty_ranges = true;
do{
if(comp(*first_min, *first1)) {
op(three_way_t(), first2++, first_min++, d_first++);
non_empty_ranges = first2 != last2;
}
else{
op(first1++, d_first++);
non_empty_ranges = first1 != last1;
}
} while(non_empty_ranges);
r_first_min = first_min;
r_first1 = first1;
r_first2 = first2;
}
return d_first;
}

template<class RandIt, class InputIt2, class OutputIt, class Compare, class Op>
OutputIt op_partial_merge_and_swap
(RandIt &r_first1, RandIt const last1, InputIt2 &r_first2, InputIt2 const last2, InputIt2 &r_first_min, OutputIt d_first, Compare comp, Op op, bool is_stable)
{
return is_stable ? op_partial_merge_and_swap_impl(r_first1, last1, r_first2, last2, r_first_min, d_first, comp, op)
: op_partial_merge_and_swap_impl(r_first1, last1, r_first2, last2, r_first_min, d_first, antistable<Compare>(comp), op);
}

template<class RandIt1, class RandIt2, class RandItB, class Compare, class Op>
RandItB op_buffered_partial_merge_and_swap_to_range1_and_buffer
( RandIt1 first1, RandIt1 const last1
, RandIt2 &rfirst2, RandIt2 const last2, RandIt2 &rfirst_min
, RandItB &rfirstb, Compare comp, Op op )
{
RandItB firstb = rfirstb;
RandItB lastb  = firstb;
RandIt2 first2 = rfirst2;

//Move to buffer while merging
//Three way moves need less moves when op is swap_op so use it
//when merging elements from range2 to the destination occupied by range1
if(first1 != last1 && first2 != last2){
RandIt2 first_min = rfirst_min;
op(four_way_t(), first2++, first_min++, first1++, lastb++);

while(first1 != last1){
if(first2 == last2){
lastb = op(forward_t(), first1, last1, firstb);
break;
}

if(comp(*first_min, *firstb)){
op( four_way_t(), first2++, first_min++, first1++, lastb++);
}
else{
op(three_way_t(), firstb++, first1++, lastb++);
}
}
rfirst2 = first2;
rfirstb = firstb;
rfirst_min = first_min;
}

return lastb;
}

template<class RandIt1, class RandIt2, class RandItB, class Compare, class Op>
RandItB op_buffered_partial_merge_to_range1_and_buffer
( RandIt1 first1, RandIt1 const last1
, RandIt2 &rfirst2, RandIt2 const last2
, RandItB &rfirstb, Compare comp, Op op )
{
RandItB firstb = rfirstb;
RandItB lastb  = firstb;
RandIt2 first2 = rfirst2;

//Move to buffer while merging
//Three way moves need less moves when op is swap_op so use it
//when merging elements from range2 to the destination occupied by range1
if(first1 != last1 && first2 != last2){
op(three_way_t(), first2++, first1++, lastb++);

while(true){
if(first1 == last1){
break;
}
if(first2 == last2){
lastb = op(forward_t(), first1, last1, firstb);
break;
}
if (comp(*first2, *firstb)) {
op(three_way_t(), first2++, first1++, lastb++);
}
else {
op(three_way_t(), firstb++, first1++, lastb++);
}
}
rfirst2 = first2;
rfirstb = firstb;
}

return lastb;
}

template<class RandIt, class RandItBuf, class Compare, class Op>
RandIt op_partial_merge_and_save_impl
( RandIt first1, RandIt const last1, RandIt &rfirst2, RandIt last2, RandIt first_min
, RandItBuf &buf_first1_in_out, RandItBuf &buf_last1_in_out
, Compare comp, Op op
)
{
RandItBuf buf_first1 = buf_first1_in_out;
RandItBuf buf_last1  = buf_last1_in_out;
RandIt first2(rfirst2);

bool const do_swap = first2 != first_min;
if(buf_first1 == buf_last1){
//Skip any element that does not need to be moved
RandIt new_first1 = skip_until_merge(first1, last1, *first_min, comp);
buf_first1 += (new_first1-first1);
first1 = new_first1;
buf_last1  = do_swap ? op_buffered_partial_merge_and_swap_to_range1_and_buffer(first1, last1, first2, last2, first_min, buf_first1, comp, op)
: op_buffered_partial_merge_to_range1_and_buffer    (first1, last1, first2, last2, buf_first1, comp, op);
first1 = last1;
}
else{
BOOST_ASSERT((last1-first1) == (buf_last1 - buf_first1));
}

//Now merge from buffer
first1 = do_swap ? op_partial_merge_and_swap_impl(buf_first1, buf_last1, first2, last2, first_min, first1, comp, op)
: op_partial_merge_impl    (buf_first1, buf_last1, first2, last2, first1, comp, op);
buf_first1_in_out = buf_first1;
buf_last1_in_out  = buf_last1;
rfirst2 = first2;
return first1;
}

template<class RandIt, class RandItBuf, class Compare, class Op>
RandIt op_partial_merge_and_save
( RandIt first1, RandIt const last1, RandIt &rfirst2, RandIt last2, RandIt first_min
, RandItBuf &buf_first1_in_out
, RandItBuf &buf_last1_in_out
, Compare comp
, Op op
, bool is_stable)
{
return is_stable
? op_partial_merge_and_save_impl
(first1, last1, rfirst2, last2, first_min, buf_first1_in_out, buf_last1_in_out, comp, op)
: op_partial_merge_and_save_impl
(first1, last1, rfirst2, last2, first_min, buf_first1_in_out, buf_last1_in_out, antistable<Compare>(comp), op)
;
}

//////////////////////////////////
//////////////////////////////////
//////////////////////////////////
//
//    op_merge_blocks_with_irreg
//
//////////////////////////////////
//////////////////////////////////
//////////////////////////////////

template<class RandItKeys, class KeyCompare, class RandIt, class RandIt2, class OutputIt, class Compare, class Op>
OutputIt op_merge_blocks_with_irreg
( RandItKeys key_first
, RandItKeys key_mid
, KeyCompare key_comp
, RandIt first_reg
, RandIt2 &first_irr
, RandIt2 const last_irr
, OutputIt dest
, typename iterator_traits<RandIt>::size_type const l_block
, typename iterator_traits<RandIt>::size_type n_block_left
, typename iterator_traits<RandIt>::size_type min_check
, typename iterator_traits<RandIt>::size_type max_check
, Compare comp, bool const is_stable, Op op)
{
typedef typename iterator_traits<RandIt>::size_type size_type;

for(; n_block_left; --n_block_left, ++key_first, min_check -= min_check != 0, max_check -= max_check != 0){
size_type next_key_idx = find_next_block(key_first, key_comp, first_reg, l_block, min_check, max_check, comp);
max_check = min_value<size_type>(max_value<size_type>(max_check, next_key_idx+size_type(2)), n_block_left);
RandIt const last_reg  = first_reg + l_block;
RandIt first_min = first_reg + next_key_idx*l_block;
RandIt const last_min  = first_min + l_block;
boost::ignore_unused(last_min);

OutputIt orig_dest = dest;
boost::ignore_unused(orig_dest);
dest = next_key_idx ? op_partial_merge_and_swap(first_irr, last_irr, first_reg, last_reg, first_min, dest, comp, op, is_stable)
: op_partial_merge         (first_irr, last_irr, first_reg, last_reg, dest, comp, op, is_stable);

if(first_reg == dest){
dest = next_key_idx ? ::boost::adl_move_swap_ranges(first_min, last_min, first_reg)
: last_reg;
}
else{
dest = next_key_idx ? op(three_way_forward_t(), first_reg, last_reg, first_min, dest)
: op(forward_t(), first_reg, last_reg, dest);
}

RandItKeys const key_next(key_first + next_key_idx);
swap_and_update_key(key_next, key_first, key_mid, last_reg, last_reg, first_min);

first_reg = last_reg;
}
return dest;
}

//////////////////////////////////
//////////////////////////////////
//////////////////////////////////
//
//    op_merge_blocks_left/right
//
//////////////////////////////////
//////////////////////////////////
//////////////////////////////////

template<class RandItKeys, class KeyCompare, class RandIt, class Compare, class Op>
void op_merge_blocks_left
( RandItKeys const key_first
, KeyCompare key_comp
, RandIt const first
, typename iterator_traits<RandIt>::size_type const l_block
, typename iterator_traits<RandIt>::size_type const l_irreg1
, typename iterator_traits<RandIt>::size_type const n_block_a
, typename iterator_traits<RandIt>::size_type const n_block_b
, typename iterator_traits<RandIt>::size_type const l_irreg2
, Compare comp, Op op)
{
typedef typename iterator_traits<RandIt>::size_type size_type;
size_type const key_count = needed_keys_count(n_block_a, n_block_b);
boost::ignore_unused(key_count);

//   BOOST_ASSERT(n_block_a || n_block_b);
BOOST_MOVE_ADAPTIVE_SORT_INVARIANT(!n_block_b || n_block_a == count_if_with(key_first, key_first + key_count, key_comp, key_first[n_block_a]));

size_type n_block_b_left = n_block_b;
size_type n_block_a_left = n_block_a;
size_type n_block_left = n_block_b + n_block_a;
RandItKeys key_mid(key_first + n_block_a);

RandIt buffer = first - l_block;
RandIt first1 = first;
RandIt last1  = first1 + l_irreg1;
RandIt first2 = last1;
RandIt const irreg2 = first2 + n_block_left*l_block;
bool is_range1_A = true;

RandItKeys key_range2(key_first);

////////////////////////////////////////////////////////////////////////////
//Process all regular blocks before the irregular B block
////////////////////////////////////////////////////////////////////////////
size_type min_check = n_block_a == n_block_left ? 0u : n_block_a;
size_type max_check = min_value<size_type>(min_check+size_type(1), n_block_left);
for (; n_block_left; --n_block_left, ++key_range2, min_check -= min_check != 0, max_check -= max_check != 0) {
size_type const next_key_idx = find_next_block(key_range2, key_comp, first2, l_block, min_check, max_check, comp);
max_check = min_value<size_type>(max_value<size_type>(max_check, next_key_idx+size_type(2)), n_block_left);
RandIt const first_min = first2 + next_key_idx*l_block;
RandIt const last_min  = first_min + l_block;

boost::ignore_unused(last_min);
RandIt const last2  = first2 + l_block;

//Check if irregular b block should go here.
//If so, break to the special code handling the irregular block
if (!n_block_b_left &&
( (l_irreg2 && comp(*irreg2, *first_min)) || (!l_irreg2 && is_range1_A)) ){
break;
}

RandItKeys const key_next(key_range2 + next_key_idx);
bool const is_range2_A = key_mid == (key_first+key_count) || key_comp(*key_next, *key_mid);

bool const is_buffer_middle = last1 == buffer;
BOOST_MOVE_ADAPTIVE_SORT_INVARIANT( ( is_buffer_middle && size_type(first2-buffer) == l_block && buffer == last1) ||
(!is_buffer_middle && size_type(first1-buffer) == l_block && first2 == last1));

if(is_range1_A == is_range2_A){
BOOST_ASSERT((first1 == last1) || !comp(*first_min, last1[-1]));
if(!is_buffer_middle){
buffer = op(forward_t(), first1, last1, buffer);
}
swap_and_update_key(key_next, key_range2, key_mid, first2, last2, first_min);
first1 = first2;
last1  = last2;
}
else {
RandIt unmerged;
RandIt buf_beg;
RandIt buf_end;
if(is_buffer_middle){
buf_end = buf_beg = first2 - (last1-first1);
unmerged = op_partial_merge_and_save( first1, last1, first2, last2, first_min
, buf_beg, buf_end, comp, op, is_range1_A);
}
else{
buf_beg = first1;
buf_end = last1;
unmerged = op_partial_merge_and_save
(buffer, buffer+(last1-first1), first2, last2, first_min, buf_beg, buf_end, comp, op, is_range1_A);
}

boost::ignore_unused(unmerged);

swap_and_update_key( key_next, key_range2, key_mid, first2, last2
, last_min - size_type(last2 - first2));

if(buf_beg != buf_end){  //range2 exhausted: is_buffer_middle for the next iteration
first1 = buf_beg;
last1  = buf_end;
buffer = last1;
}
else{ //range1 exhausted: !is_buffer_middle for the next iteration
first1 = first2;
last1  = last2;
buffer = first2 - l_block;
is_range1_A = is_range2_A;
}
}
BOOST_MOVE_ADAPTIVE_SORT_INVARIANT( (is_range2_A && n_block_a_left) || (!is_range2_A && n_block_b_left));
is_range2_A ? --n_block_a_left : --n_block_b_left;
first2 = last2;
}

BOOST_MOVE_ADAPTIVE_SORT_INVARIANT(!n_block_b || n_block_a == count_if_with(key_first, key_range2 + n_block_left, key_comp, *key_mid));
BOOST_ASSERT(!n_block_b_left);

////////////////////////////////////////////////////////////////////////////
//Process remaining range 1 left before the irregular B block
////////////////////////////////////////////////////////////////////////////
bool const is_buffer_middle = last1 == buffer;
RandIt first_irr2 = irreg2;
RandIt const last_irr2  = first_irr2 + l_irreg2;
if(l_irreg2 && is_range1_A){
if(is_buffer_middle){
first1 = skip_until_merge(first1, last1, *first_irr2, comp);
//Even if we copy backward, no overlapping occurs so use forward copy
//that can be faster specially with trivial types
RandIt const new_first1 = first2 - (last1 - first1);
op(forward_t(), first1, last1, new_first1);
first1 = new_first1;
last1 = first2;
buffer = first1 - l_block;
}
buffer = op_partial_merge_impl(first1, last1, first_irr2, last_irr2, buffer, comp, op);
buffer = op(forward_t(), first1, last1, buffer);
}
else if(!is_buffer_middle){
buffer = op(forward_t(), first1, last1, buffer);
}

////////////////////////////////////////////////////////////////////////////
//Process irregular B block and remaining A blocks
////////////////////////////////////////////////////////////////////////////
buffer = op_merge_blocks_with_irreg
( key_range2, key_mid, key_comp, first2, first_irr2, last_irr2
, buffer, l_block, n_block_left, min_check, max_check, comp, false, op);
buffer = op(forward_t(), first_irr2, last_irr2, buffer);
boost::ignore_unused(buffer);
}

// first - first element to merge.
// first[-l_block, 0) - buffer (if use_buf == true)
// l_block - length of regular blocks. First nblocks are stable sorted by 1st elements and key-coded
// keys - sequence of keys, in same order as blocks. key<midkey means stream A
// n_bef_irreg2/n_aft_irreg2 are regular blocks
// l_irreg2 is a irregular block, that is to be combined after n_bef_irreg2 blocks and before n_aft_irreg2 blocks
// If l_irreg2==0 then n_aft_irreg2==0 (no irregular blocks).
template<class RandItKeys, class KeyCompare, class RandIt, class Compare>
void merge_blocks_left
( RandItKeys const key_first
, KeyCompare key_comp
, RandIt const first
, typename iterator_traits<RandIt>::size_type const l_block
, typename iterator_traits<RandIt>::size_type const l_irreg1
, typename iterator_traits<RandIt>::size_type const n_block_a
, typename iterator_traits<RandIt>::size_type const n_block_b
, typename iterator_traits<RandIt>::size_type const l_irreg2
, Compare comp
, bool const xbuf_used)
{
BOOST_MOVE_ADAPTIVE_SORT_INVARIANT(!n_block_b || n_block_a == count_if_with(key_first, key_first + needed_keys_count(n_block_a, n_block_b), key_comp, key_first[n_block_a]));
if(xbuf_used){
op_merge_blocks_left
(key_first, key_comp, first, l_block, l_irreg1, n_block_a, n_block_b, l_irreg2, comp, move_op());
}
else{
op_merge_blocks_left
(key_first, key_comp, first, l_block, l_irreg1, n_block_a, n_block_b, l_irreg2, comp, swap_op());
}
}

// first - first element to merge.
// [first+l_block*(n_bef_irreg2+n_aft_irreg2)+l_irreg2, first+l_block*(n_bef_irreg2+n_aft_irreg2+1)+l_irreg2) - buffer
// l_block - length of regular blocks. First nblocks are stable sorted by 1st elements and key-coded
// keys - sequence of keys, in same order as blocks. key<midkey means stream A
// n_bef_irreg2/n_aft_irreg2 are regular blocks
// l_irreg2 is a irregular block, that is to be combined after n_bef_irreg2 blocks and before n_aft_irreg2 blocks
// If l_irreg2==0 then n_aft_irreg2==0 (no irregular blocks).
template<class RandItKeys, class KeyCompare, class RandIt, class Compare>
void merge_blocks_right
( RandItKeys const key_first
, KeyCompare key_comp
, RandIt const first
, typename iterator_traits<RandIt>::size_type const l_block
, typename iterator_traits<RandIt>::size_type const n_block_a
, typename iterator_traits<RandIt>::size_type const n_block_b
, typename iterator_traits<RandIt>::size_type const l_irreg2
, Compare comp
, bool const xbuf_used)
{
merge_blocks_left
( (make_reverse_iterator)(key_first + needed_keys_count(n_block_a, n_block_b))
, inverse<KeyCompare>(key_comp)
, (make_reverse_iterator)(first + ((n_block_a+n_block_b)*l_block+l_irreg2))
, l_block
, l_irreg2
, n_block_b
, n_block_a
, 0
, inverse<Compare>(comp), xbuf_used);
}

//////////////////////////////////
//////////////////////////////////
//////////////////////////////////
//
//    op_merge_blocks_with_buf
//
//////////////////////////////////
//////////////////////////////////
//////////////////////////////////
template<class RandItKeys, class KeyCompare, class RandIt, class Compare, class Op, class RandItBuf>
void op_merge_blocks_with_buf
( RandItKeys key_first
, KeyCompare key_comp
, RandIt const first
, typename iterator_traits<RandIt>::size_type const l_block
, typename iterator_traits<RandIt>::size_type const l_irreg1
, typename iterator_traits<RandIt>::size_type const n_block_a
, typename iterator_traits<RandIt>::size_type const n_block_b
, typename iterator_traits<RandIt>::size_type const l_irreg2
, Compare comp
, Op op
, RandItBuf const buf_first)
{
typedef typename iterator_traits<RandIt>::size_type size_type;
size_type const key_count = needed_keys_count(n_block_a, n_block_b);
boost::ignore_unused(key_count);
//BOOST_ASSERT(n_block_a || n_block_b);
BOOST_MOVE_ADAPTIVE_SORT_INVARIANT(!n_block_b || n_block_a == count_if_with(key_first, key_first + key_count, key_comp, key_first[n_block_a]));

size_type n_block_b_left = n_block_b;
size_type n_block_a_left = n_block_a;
size_type n_block_left = n_block_b + n_block_a;
RandItKeys key_mid(key_first + n_block_a);

RandItBuf buffer = buf_first;
RandItBuf buffer_end = buffer;
RandIt first1 = first;
RandIt last1  = first1 + l_irreg1;
RandIt first2 = last1;
RandIt const first_irr2 = first2 + n_block_left*l_block;
bool is_range1_A = true;
const size_type len = l_block * n_block_a + l_block * n_block_b + l_irreg1 + l_irreg2;
boost::ignore_unused(len);

RandItKeys key_range2(key_first);

////////////////////////////////////////////////////////////////////////////
//Process all regular blocks before the irregular B block
////////////////////////////////////////////////////////////////////////////
size_type min_check = n_block_a == n_block_left ? 0u : n_block_a;
size_type max_check = min_value<size_type>(min_check+size_type(1), n_block_left);
for (; n_block_left; --n_block_left, ++key_range2, min_check -= min_check != 0, max_check -= max_check != 0) {
size_type const next_key_idx = find_next_block(key_range2, key_comp, first2, l_block, min_check, max_check, comp);
max_check = min_value<size_type>(max_value<size_type>(max_check, next_key_idx+size_type(2)), n_block_left);
RandIt       first_min = first2 + next_key_idx*l_block;
RandIt const last_min  = first_min + l_block;
boost::ignore_unused(last_min);
RandIt const last2  = first2 + l_block;

bool const buffer_empty = buffer == buffer_end;
boost::ignore_unused(buffer_empty);
BOOST_MOVE_ADAPTIVE_SORT_INVARIANT(buffer_empty ? boost::movelib::is_sorted(first1, last1, comp) : boost::movelib::is_sorted(buffer, buffer_end, comp));

//Check if irregular b block should go here.
//If so, break to the special code handling the irregular block
if (!n_block_b_left &&
( (l_irreg2 && comp(*first_irr2, *first_min)) || (!l_irreg2 && is_range1_A)) ){
break;
}

RandItKeys const key_next(key_range2 + next_key_idx);
bool const is_range2_A = key_mid == (key_first+key_count) || key_comp(*key_next, *key_mid);

if(is_range1_A == is_range2_A){
BOOST_MOVE_ADAPTIVE_SORT_INVARIANT((first1 == last1) || (buffer_empty ? !comp(*first_min, last1[-1]) : !comp(*first_min, buffer_end[-1])));
//If buffered, put those elements in place
RandIt res = op(forward_t(), buffer, buffer_end, first1);
buffer    = buffer_end = buf_first;
BOOST_ASSERT(buffer_empty || res == last1);
boost::ignore_unused(res);
//swap_and_update_key(key_next, key_range2, key_mid, first2, last2, first_min);
buffer_end = buffer_and_update_key(key_next, key_range2, key_mid, first2, last2, first_min, buffer = buf_first, op);
first1 = first2;
}
else {
RandIt const unmerged = op_partial_merge_and_save(first1, last1, first2, last2, first_min, buffer, buffer_end, comp, op, is_range1_A);
bool const is_range_1_empty = buffer == buffer_end;
BOOST_ASSERT(is_range_1_empty || (buffer_end-buffer) == (last1+l_block-unmerged));
if(is_range_1_empty){
buffer    = buffer_end = buf_first;
first_min = last_min - (last2 - first2);
//swap_and_update_key(key_next, key_range2, key_mid, first2, last2, first_min);
buffer_end = buffer_and_update_key(key_next, key_range2, key_mid, first2, last2, first_min, buf_first, op);
}
else{
first_min = last_min;
//swap_and_update_key(key_next, key_range2, key_mid, first2, last2, first_min);
update_key(key_next, key_range2, key_mid);
}
is_range1_A ^= is_range_1_empty;
first1 = unmerged;
}
BOOST_ASSERT( (is_range2_A && n_block_a_left) || (!is_range2_A && n_block_b_left));
is_range2_A ? --n_block_a_left : --n_block_b_left;
last1 += l_block;
first2 = last2;
}
RandIt res = op(forward_t(), buffer, buffer_end, first1);
boost::ignore_unused(res);

////////////////////////////////////////////////////////////////////////////
//Process irregular B block and remaining A blocks
////////////////////////////////////////////////////////////////////////////
RandIt const last_irr2 = first_irr2 + l_irreg2;
op(forward_t(), first_irr2, first_irr2+l_irreg2, buf_first);
buffer = buf_first;
buffer_end = buffer+l_irreg2;

reverse_iterator<RandItBuf> rbuf_beg(buffer_end);
RandIt dest = op_merge_blocks_with_irreg
((make_reverse_iterator)(key_first + n_block_b + n_block_a), (make_reverse_iterator)(key_mid), inverse<KeyCompare>(key_comp)
, (make_reverse_iterator)(first_irr2), rbuf_beg, (make_reverse_iterator)(buffer), (make_reverse_iterator)(last_irr2)
, l_block, n_block_left, 0, n_block_left
, inverse<Compare>(comp), true, op).base();

buffer_end = rbuf_beg.base();
BOOST_ASSERT((dest-last1) == (buffer_end-buffer));
op_merge_with_left_placed(is_range1_A ? first1 : last1, last1, dest, buffer, buffer_end, comp, op);
}

//////////////////////////////////
//////////////////////////////////
//////////////////////////////////
//
//  op_insertion_sort_step_left/right
//
//////////////////////////////////
//////////////////////////////////
//////////////////////////////////

template<class RandIt, class Compare, class Op>
typename iterator_traits<RandIt>::size_type
op_insertion_sort_step_left
( RandIt const first
, typename iterator_traits<RandIt>::size_type const length
, typename iterator_traits<RandIt>::size_type const step
, Compare comp, Op op)
{
typedef typename iterator_traits<RandIt>::size_type size_type;
size_type const s = min_value<size_type>(step, AdaptiveSortInsertionSortThreshold);
size_type m = 0;

while((length - m) > s){
insertion_sort_op(first+m, first+m+s, first+m-s, comp, op);
m += s;
}
insertion_sort_op(first+m, first+length, first+m-s, comp, op);
return s;
}

template<class RandIt, class Compare, class Op>
void op_merge_right_step_once
( RandIt first_block
, typename iterator_traits<RandIt>::size_type const elements_in_blocks
, typename iterator_traits<RandIt>::size_type const l_build_buf
, Compare comp
, Op op)
{
typedef typename iterator_traits<RandIt>::size_type size_type;
size_type restk = elements_in_blocks%(2*l_build_buf);
size_type p = elements_in_blocks - restk;
BOOST_ASSERT(0 == (p%(2*l_build_buf)));

if(restk <= l_build_buf){
op(backward_t(),first_block+p, first_block+p+restk, first_block+p+restk+l_build_buf);
}
else{
op_merge_right(first_block+p, first_block+p+l_build_buf, first_block+p+restk, first_block+p+restk+l_build_buf, comp, op);
}
while(p>0){
p -= 2*l_build_buf;
op_merge_right(first_block+p, first_block+p+l_build_buf, first_block+p+2*l_build_buf, first_block+p+3*l_build_buf, comp, op);
}
}

//////////////////////////////////
//////////////////////////////////
//////////////////////////////////
//
//    insertion_sort_step
//
//////////////////////////////////
//////////////////////////////////
//////////////////////////////////
template<class RandIt, class Compare>
typename iterator_traits<RandIt>::size_type
insertion_sort_step
( RandIt const first
, typename iterator_traits<RandIt>::size_type const length
, typename iterator_traits<RandIt>::size_type const step
, Compare comp)
{
typedef typename iterator_traits<RandIt>::size_type size_type;
size_type const s = min_value<size_type>(step, AdaptiveSortInsertionSortThreshold);
size_type m = 0;

while((length - m) > s){
insertion_sort(first+m, first+m+s, comp);
m += s;
}
insertion_sort(first+m, first+length, comp);
return s;
}

//////////////////////////////////
//////////////////////////////////
//////////////////////////////////
//
//    op_merge_left_step_multiple
//
//////////////////////////////////
//////////////////////////////////
//////////////////////////////////
template<class RandIt, class Compare, class Op>
typename iterator_traits<RandIt>::size_type
op_merge_left_step_multiple
( RandIt first_block
, typename iterator_traits<RandIt>::size_type const elements_in_blocks
, typename iterator_traits<RandIt>::size_type l_merged
, typename iterator_traits<RandIt>::size_type const l_build_buf
, typename iterator_traits<RandIt>::size_type l_left_space
, Compare comp
, Op op)
{
typedef typename iterator_traits<RandIt>::size_type size_type;
for(; l_merged < l_build_buf && l_left_space >= l_merged; l_merged*=2){
size_type p0=0;
RandIt pos = first_block;
while((elements_in_blocks - p0) > 2*l_merged) {
op_merge_left(pos-l_merged, pos, pos+l_merged, pos+2*l_merged, comp, op);
p0 += 2*l_merged;
pos = first_block+p0;
}
if((elements_in_blocks-p0) > l_merged) {
op_merge_left(pos-l_merged, pos, pos+l_merged, first_block+elements_in_blocks, comp, op);
}
else {
op(forward_t(), pos, first_block+elements_in_blocks, pos-l_merged);
}
first_block -= l_merged;
l_left_space -= l_merged;
}
return l_merged;
}