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Make dmsort work with bidirectional iterators #6

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Make dmsort work with bidirectional iterators #6

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32 changes: 15 additions & 17 deletions drop_merge_sort.hpp
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Original file line number Diff line number Diff line change
Expand Up @@ -30,9 +30,7 @@ namespace detail {
// with-trivial-copies version
template<typename Iter, typename Comp>
void dmsort(Iter begin, Iter end, Comp comp, std::true_type) {
size_t size = end - begin;

if (size < 2)
if (begin == end || std::next(begin) == end)
return;

using Value = typename std::iterator_traits<Iter>::value_type;
Expand All @@ -45,11 +43,12 @@ namespace detail {
constexpr size_t recency = 8;

while (read != end) {
if (begin != write && comp(*read, *(write - 1))) {
if (begin != write && comp(*read, *std::prev(write))) {

if (double_comparison && num_dropped_in_row == 0 && write > begin+1 && !comp(*read, *(write-2))) {
dropped.push_back(*(write-1));
*(write-1) = *read;
if (double_comparison && num_dropped_in_row == 0 && write != std::next(begin)
&& !comp(*read, *std::prev(write, 2))) {
dropped.push_back(*std::prev(write));
*std::prev(write) = *read;
++read;
continue;
}
Expand All @@ -62,7 +61,7 @@ namespace detail {
for (int i = 0; i < num_dropped_in_row; ++i) {
dropped.pop_back();
}
read -= num_dropped_in_row;
std::advance(read, -num_dropped_in_row);

--write;
dropped.push_back(*write);
Expand All @@ -86,7 +85,7 @@ namespace detail {
while (!dropped.empty()) {
auto & last_dropped = dropped.back();

while (begin != write && comp(last_dropped, *(write - 1))) {
while (begin != write && comp(last_dropped, *std::prev(write))) {
--back;
--write;
*back = std::move(*write);
Expand All @@ -100,9 +99,7 @@ namespace detail {
// move-only version
template<typename Iter, typename Comp>
void dmsort(Iter begin, Iter end, Comp comp, std::false_type) {
size_t size = end - begin;

if (size < 2)
if (begin == end || std::next(begin) == end)
return;

using Value = typename std::iterator_traits<Iter>::value_type;
Expand All @@ -115,11 +112,12 @@ namespace detail {
constexpr size_t recency = 8;

while (read != end) {
if (begin != write && comp(*read, *(write - 1))) {
if (begin != write && comp(*read, *std::prev(write))) {

if (double_comparison && num_dropped_in_row == 0 && write > begin+1 && !comp(*read, *(write-2))) {
dropped.push_back(std::move(*(write-1)));
*(write-1) = std::move(*read);
if (double_comparison && num_dropped_in_row == 0 && write != std::next(begin)
&& !comp(*read, *std::prev(write, 2))) {
dropped.push_back(std::move(*std::prev(write)));
*std::prev(write) = std::move(*read);
++read;
continue;
}
Expand Down Expand Up @@ -157,7 +155,7 @@ namespace detail {
while (!dropped.empty()) {
auto & last_dropped = dropped.back();

while (begin != write && comp(last_dropped, *(write - 1))) {
while (begin != write && comp(last_dropped, *std::prev(write))) {
--back;
--write;
*back = std::move(*write);
Expand Down
28 changes: 26 additions & 2 deletions tests.cpp
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Original file line number Diff line number Diff line change
@@ -1,7 +1,10 @@
#include <vector>
#include <iostream>
#include <algorithm>
#include <iomanip>
#include <iostream>
#include <list>
#include <memory>
#include <random>
#include <vector>
#include "drop_merge_sort.hpp"

/*
Expand Down Expand Up @@ -59,6 +62,24 @@ void test_counts(){
PRINT(moveass);
}

/*
Check that dmsort can sort bidirectional iterators
*/

void test_list(){
std::vector<int> vec;
for(int i = 0; i < 500000; ++i)
vec.push_back(i);

// Create a shuffled list
std::minstd_rand engine(123456);
std::shuffle(vec.begin(), vec.end(), engine);
std::list<int> li(vec.begin(), vec.end());

dmsort(li.begin(), li.end());
std::cout << std::is_sorted(li.begin(), li.end()) << std::endl;
}

/*
Check that the move-only version actually works with move-only types
*/
Expand Down Expand Up @@ -106,7 +127,10 @@ void test_non_default_constructible(){
}

int main(){
std::cout << std::boolalpha;

test_counts();
test_list();
test_noncopyable();
test_non_default_constructible();
}