java-topology/defects/kicad/patch/kicad-0002-zone-filler-hashset.md

UNDF: UNDF-2026-000000589

kicad-0002: zone_filler.cpp std::find O(Z²×L²) → O(Z×L log(Z×L)) with ordered set

Classification

Field	Value
CWE	CWE-407 Inefficient Algorithmic Complexity
Severity	MEDIUM
Component	pcbnew/zone_filler.cpp:998
Function	ZONE_FILLER::Fill() — iterative refill with removed islands
Hot path	Zone fill / DRC with copper island removal on complex boards
Status	PATCHED (unit test PASS)

Defect

The iterative refill path accumulates zones needing refill in a std::vector and uses std::find O(N) for deduplication inside a triple nested loop:

// zone_filler.cpp:998
std::vector<std::pair<ZONE*, PCB_LAYER_ID>> zonesToRefill;

for( ZONE* zoneWithIsland : zonesWithRemovedIslands )     // Z_r removed-island zones
{
    for( ZONE* zone : aZones )                            // Z total zones
    {
        for( PCB_LAYER_ID layer : commonLayers )          // L copper layers
        {
            auto fillItem = std::make_pair( zone, layer );
            if( std::find( zonesToRefill.begin(),
                           zonesToRefill.end(), fillItem ) // O(Z×L) linear scan
                    == zonesToRefill.end() )
                zonesToRefill.push_back( fillItem );
        }
    }
}

With Z=50 zones, L=4 layers, Z_r=10 zones with islands:

• Before: 10 × 50 × 4 × (50×4) = 400,000 comparisons per refill pass
• After: 10 × 50 × 4 × O(1) = 2,000 operations (200×)

Fix

Replace std::vector with std::set<std::pair<ZONE*, PCB_LAYER_ID>> or std::unordered_set with a custom hash:

struct PairHash {
    size_t operator()(const std::pair<ZONE*, PCB_LAYER_ID>& p) const {
        return std::hash<ZONE*>()(p.first) ^ (std::hash<int>()(p.second) << 16);
    }
};
std::unordered_set<std::pair<ZONE*, PCB_LAYER_ID>, PairHash> zonesToRefill;

// Insert: O(1) average — dedup is automatic
zonesToRefill.insert( std::make_pair( zone, layer ) );

Convert back to std::vector for the subsequent Fill call if needed.

Speedup: ~200× at Z=50, L=4.