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Replace call to 'iota' with hand-rolled loop

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This commit is contained in:
Marshall Clow
2023-06-25 20:20:45 -07:00
parent a7ae53d615
commit 25ab833cae
1 changed files with 21 additions and 13 deletions
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34
include/boost/algorithm/indirect_sort.hpp
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@ -18,10 +18,10 @@
#include <functional> // for std::less
#include <vector> // for std::vector
#include <boost/algorithm/cxx11/iota.hpp>
namespace boost { namespace algorithm {
typedef std::vector<size_t> Permutation;
namespace detail {
template <class Predicate, class Iter>
@ -37,10 +37,18 @@ namespace detail {
Iter iter_;
};
// Initialize a permutation
// it would be nice to use 'iota' here, but that call writes over
// existing elements - not append them. I don't want to initialize
// the elements of the permutation to zero, and then immediately
// overwrite them.
void init_permutation (Permutation &p, size_t size) {
p.reserve(size);
for (size_t i = 0; i < size; ++i)
p.push_back(i);
}
}
typedef std::vector<size_t> Permutation;
// ===== sort =====
/// \fn indirect_sort (RAIterator first, RAIterator last, Predicate pred)
@ -55,8 +63,9 @@ typedef std::vector<size_t> Permutation;
///
template <typename RAIterator, typename Pred>
Permutation indirect_sort (RAIterator first, RAIterator last, Pred pred) {
Permutation ret(std::distance(first, last));
boost::algorithm::iota(ret.begin(), ret.end(), size_t(0));
Permutation ret;
detail::init_permutation(ret, std::distance(first, last));
std::sort(ret.begin(), ret.end(),
detail::indirect_predicate<Pred, RAIterator>(pred, first));
return ret;
@ -91,8 +100,8 @@ Permutation indirect_sort (RAIterator first, RAIterator last) {
///
template <typename RAIterator, typename Pred>
Permutation indirect_stable_sort (RAIterator first, RAIterator last, Pred pred) {
Permutation ret(std::distance(first, last));
boost::algorithm::iota(ret.begin(), ret.end(), size_t(0));
Permutation ret;
detail::init_permutation(ret, std::distance(first, last));
std::stable_sort(ret.begin(), ret.end(),
detail::indirect_predicate<Pred, RAIterator>(pred, first));
return ret;
@ -129,9 +138,8 @@ Permutation indirect_stable_sort (RAIterator first, RAIterator last) {
template <typename RAIterator, typename Pred>
Permutation indirect_partial_sort (RAIterator first, RAIterator middle,
RAIterator last, Pred pred) {
Permutation ret(std::distance(first, last));
boost::algorithm::iota(ret.begin(), ret.end(), size_t(0));
Permutation ret;
detail::init_permutation(ret, std::distance(first, last));
std::partial_sort(ret.begin(), ret.begin() + std::distance(first, middle), ret.end(),
detail::indirect_predicate<Pred, RAIterator>(pred, first));
return ret;
@ -169,8 +177,8 @@ Permutation indirect_partial_sort (RAIterator first, RAIterator middle, RAIterat
template <typename RAIterator, typename Pred>
Permutation indirect_nth_element (RAIterator first, RAIterator nth,
RAIterator last, Pred pred) {
Permutation ret(std::distance(first, last));
boost::algorithm::iota(ret.begin(), ret.end(), size_t(0));
Permutation ret;
detail::init_permutation(ret, std::distance(first, last));
std::nth_element(ret.begin(), ret.begin() + std::distance(first, nth), ret.end(),
detail::indirect_predicate<Pred, RAIterator>(pred, first));
return ret;