amorfo77/json
1
0 Fork 0
mirror of https://github.com/nlohmann/json.git synced 2026-10-11 08:57:15 +00:00
Code Issues Packages Projects Releases Wiki Activity

Replace a container by a scalar in constant time once it is linked

Browse Source 
Replacing an array or object that spans several nodes by a scalar looks
up its parent from the root (find_parent), which is linear in the size
of the document: setting every element of a 20,000 element array took
more than half a second. The parent only has to switch to links once;
afterward the extent of the replaced value no longer matters. Nodes that
an entry of a moved sequence links to are now marked (node_flags::linked),
and assign() skips the lookup for them.

Signed-off-by: Niels Lohmann <mail@nlohmann.me>
This commit is contained in:
Niels Lohmann committed 2026-10-11 10:28:36 +02:00
1 parent 5d5f03d858
commit 045f2facdc
5 files changed
+62 -8
Download Patch File Download Diff File Expand all files Collapse all files

No files matched your search

include/nlohmann/detail/view/edit.hpp
+10 -4
View File
@@ -348,9 +348,10 @@ class editor
/// turn a null into an empty array/object in place
static void become_empty(node* n, value_t k) noexcept
{
const std::uint8_t linked = n->flags & node_flags::linked;
*n = node{};
n->kind = static_cast<std::uint8_t>(k);
n->flags = node_flags::is_new;
n->flags = static_cast<std::uint8_t>(node_flags::is_new | linked);
n->next = 1;
}
@@ -358,13 +359,17 @@ class editor
/// include slot (if known).
void assign(node* slot, const encoded& e, node* parent, bool parent_known)
{
// an entry of a moved sequence links to the slot: it can take any extent
const std::uint8_t linked = slot->flags & node_flags::linked;
if (e.region == nullptr)
{
if (is_container(*slot) && slot->next > 1 && slot != m_doc.tape)
if (is_container(*slot) && slot->next > 1 && slot != m_doc.tape && linked == 0)
{
// The slot spans its old elements in the enclosing sequence, but
// a scalar is one node: the enclosing container first switches to
// links (then the extent of the slot no longer matters).
// links (then the extent of the slot no longer matters). Looking
// for the container is linear in the size of the document, so
// links (which are marked in the slot) avoid it.
node* const p = parent_known ? parent : find_parent(m_doc, slot);
if (p != nullptr && ((p->flags & node_flags::moved) == 0 || moved_capacity(m_doc, p) == 0))
{
@@ -372,6 +377,7 @@ class editor
}
}
*slot = e.scalar;
slot->flags = static_cast<std::uint8_t>(slot->flags | linked);
return;
}
// an array/object: the slot keeps its extent (so that the enclosing
@@ -394,7 +400,7 @@ class editor
slot->len = r->len;
slot->next = extent;
// (set_moved() adds the moved flag to a slot that does not have it yet)
slot->flags = was_moved ? static_cast<std::uint8_t>(node_flags::moved | node_flags::is_new) : std::uint8_t{0};
slot->flags = static_cast<std::uint8_t>((was_moved ? node_flags::moved | node_flags::is_new : 0) | linked);
set_moved(m_doc, slot, e.region, 0);
edit_state_of(m_doc).regions[e.region] = slot;
}