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Sped up parsing by ~0..40%-ish #149

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b8a9d7f
sped up parsing by ~0..10%
toughengineer Nov 30, 2023
0fffbc3
sped up parsing by ~0..30%
toughengineer Aug 4, 2025
784a467
sped up parsing by ~0..40%
toughengineer Aug 4, 2025
2e81c9b
ensured correct work when `begin_array(const std::size_t)` is also used
toughengineer Aug 5, 2025
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62 changes: 58 additions & 4 deletions include/tao/json/events/set_value.hpp
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Original file line number Diff line number Diff line change
Expand Up @@ -6,6 +6,7 @@

#include <cstddef>
#include <cstdint>
#include <deque>
#include <string>
#include <string_view>
#include <utility>
Expand All @@ -22,7 +23,32 @@ namespace tao::json::events
template< template< typename... > class Traits >
struct set_basic_value
{
static constexpr size_t count_ = 42;
static constexpr size_t count_skip_bit_ = size_t{ 1 } << ( std::numeric_limits< size_t >::digits - 1 );
struct InPlaceVector
{
union
{
basic_value< Traits > array[ count_ ];
};
size_t count = 0;
InPlaceVector() {}
~InPlaceVector()
{
std::destroy_n( array, size() );
}
void emplace_back( basic_value< Traits >&& v )
{
::new( array + count ) basic_value< Traits >{ std::move( v ) };
++count;
}
size_t size() const
{
return count & ~count_skip_bit_;
}
};
std::vector< basic_value< Traits > > stack_;
std::deque< InPlaceVector > elements_;
std::vector< std::string > keys_;
basic_value< Traits >& value_;

Expand Down Expand Up @@ -96,29 +122,57 @@ namespace tao::json::events

void begin_array()
{
stack_.emplace_back( empty_array );
stack_.push_back( empty_array );
elements_.emplace_back();
}

void begin_array( const std::size_t size )
{
begin_array();
elements_.back().count |= count_skip_bit_;
stack_.back().get_array().reserve( size );
}

void element()
{
stack_.back().emplace_back( std::move( value_ ) );
auto& elements = elements_.back();
if( elements.count < count_ ) {
elements.emplace_back( std::move( value_ ) );
return;
}
auto& a = stack_.back().get_array();
if( elements.count == count_ ) {
a.reserve( count_ + 1 );
a.resize( count_ );
elements.count |= count_skip_bit_;
}
a.push_back( std::move( value_ ) );
}

void end_array( const std::size_t /*unused*/ = 0 )
{
value_ = std::move( stack_.back() );
auto& elements = elements_.back();
auto& v = stack_.back();
if( const size_t size = elements.size() ) {
auto& a = v.get_array();
if( a.empty() ) {
a.assign( std::make_move_iterator( elements.array ),
std::make_move_iterator( elements.array + size ) );
}
else {
std::copy_n( std::make_move_iterator( elements.array ),
size,
a.begin() );
}
}
value_ = std::move( v );
stack_.pop_back();
elements_.pop_back();
}

void begin_object( const std::size_t /*unused*/ = 0 )
{
stack_.emplace_back( empty_object );
stack_.push_back( empty_object );
}

void key( const std::string_view v )
Expand Down