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Hash table index for O(1) packet history lookups (#9499)

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* Use hash table for O(1) lookup of recently seen packets

* Eliminate a packet lookup during deduplication

* Infinite loop checks for find and remove

* Consolidate conditional compilation

* Exclude hash table from minimal build

* Additional comment on hash table capacity

* Unit tests for packet history changes

* Update incorrect comment about size clamp

Co-authored-by: Copilot <175728472+Copilot@users.noreply.github.com>

* Const

---------

Co-authored-by: Copilot <175728472+Copilot@users.noreply.github.com>
Co-authored-by: Ben Meadors <benmmeadors@gmail.com>
This commit is contained in:
Colby Dillion
2026-04-23 18:04:34 -05:00
committed by GitHub
co-authored by GitHub Copilot Ben Meadors
parent 837637b70c
commit 83a98c81f6
6 changed files with 1053 additions and 15 deletions
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src/mesh/PacketHistory.h
+26
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@@ -28,6 +28,22 @@ class PacketHistory
0; // Can be set in constructor, no need to recompile. Used to allocate memory for mx_recentPackets.
PacketRecord *recentPackets = NULL; // Simple and fixed in size. Debloat.
#if !MESHTASTIC_EXCLUDE_PKT_HISTORY_HASH
// Open-addressing hash table for O(1) lookup in find(), replacing the O(N) linear scan.
// Maps (sender, id) -> index into recentPackets[]. Uses linear probing with a load factor <= 0.5.
// The load factor invariant holds permanently: hashCapacity = 2 * nextPowerOf2(recentPacketsCapacity),
// and at most recentPacketsCapacity entries can ever be live (one per recentPackets[] slot).
static constexpr uint16_t HASH_EMPTY = 0xFFFF;
uint16_t *hashIndex = NULL;
uint32_t hashCapacity = 0; // Always a power of 2
uint32_t hashMask = 0; // hashCapacity - 1, for fast modular indexing
uint32_t hashSlot(NodeNum sender, PacketId id) const;
void hashInsert(NodeNum sender, PacketId id, uint16_t slotIdx);
void hashRemove(NodeNum sender, PacketId id);
void hashRebuild();
#endif
/** Find a packet record in history.
* @param sender NodeNum
* @param id PacketId
@@ -70,6 +86,16 @@ class PacketHistory
* @return true if node was indeed a relayer, false if not */
bool wasRelayer(const uint8_t relayer, const uint32_t id, const NodeNum sender, bool *wasSole = nullptr);
/**
* Check two relayers against the same packet record with a single lookup.
* Avoids redundant find() calls when checking multiple relayers for the same (id, sender) pair.
* @param r1Result set to true if relayer1 was a relayer
* @param r2Result set to true if relayer2 was a relayer
* @param r2WasSole if not nullptr, set to true if relayer2 was the sole relayer
*/
void checkRelayers(uint8_t relayer1, uint8_t relayer2, uint32_t id, NodeNum sender, bool *r1Result, bool *r2Result,
bool *r2WasSole = nullptr);
// Remove a relayer from the list of relayers of a packet in the history given an ID and sender
void removeRelayer(const uint8_t relayer, const uint32_t id, const NodeNum sender);