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// file : libbutl/prefix-map.txx -*- C++ -*-
// copyright : Copyright (c) 2014-2019 Code Synthesis Ltd
// license : MIT; see accompanying LICENSE file
LIBBUTL_MODEXPORT namespace butl //@@ MOD Clang needs this for some reason.
{
template <typename M>
auto prefix_map_common<M>::
find_sub (const key_type& k) -> std::pair<iterator, iterator>
{
const auto& c (this->key_comp ());
std::pair<iterator, iterator> r;
r.first = this->lower_bound (k);
for (r.second = r.first; r.second != this->end (); ++r.second)
{
if (!c.prefix (k, r.second->first))
break;
}
return r;
}
template <typename M>
auto prefix_map_common<M>::
find_sub (const key_type& k) const ->
std::pair<const_iterator, const_iterator>
{
const auto& c (this->key_comp ());
std::pair<const_iterator, const_iterator> r;
r.first = this->lower_bound (k);
for (r.second = r.first; r.second != this->end (); ++r.second)
{
if (!c.prefix (k, r.second->first))
break;
}
return r;
}
template <typename M>
auto prefix_map_common<M>::
find_sup (const key_type& k) -> iterator
{
// There seems to be only two possible algorithms here:
//
// 1. Iterate over the key: get progressively outer prefixes and look
// for a match in the map.
//
// 2. Iterate over entries: get the upper bound for the key and iterate
// backwards looking for a prefix.
//
// The drawback of the first approach is that we have to create a new key
// which will most likely involve a memory allocation (we can probably
// limit it to a single allocation by reusing the key instance).
//
// The drawback of the second approch is that we may have a lot of entries
// between the lower bound and the prefix (in contrast, keys normally only
// have a handful of components).
//
// Tests have shown that (2) can be significantly faster than (1).
//
#if 0
const auto& c (this->key_comp ());
for (auto i (this->upper_bound (k)), b (this->begin ()); i != b; )
{
--i;
if (c.prefix (i->first, k))
return i;
}
return this->end ();
#else
// First look for the exact match before making any copies.
//
auto i (this->find (k)), e (this->end ());
if (i == e)
{
const auto& c (this->key_comp ());
for (key_type p (k); c.prefix (p); )
{
i = this->find (p);
if (i != e)
break;
}
}
return i;
#endif
}
template <typename M>
auto prefix_map_common<M>::
find_sup (const key_type& k) const -> const_iterator
{
#if 0
const auto& c (this->key_comp ());
for (auto i (this->upper_bound (k)), b (this->begin ()); i != b; )
{
--i;
if (c.prefix (i->first, k))
return i;
}
return this->end ();
#else
auto i (this->find (k)), e (this->end ());
if (i == e)
{
const auto& c (this->key_comp ());
for (key_type p (k); c.prefix (p); )
{
i = this->find (p);
if (i != e)
break;
}
}
return i;
#endif
}
}
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