From 8f2e356db0525fb6674b6639a671f0a423cfec65 Mon Sep 17 00:00:00 2001
From: mikera <mike@mikera.net>
Date: Tue, 8 Oct 2024 06:15:23 +0100
Subject: [PATCH] Add cache for first entry hash in HashMaps

---
 convex-core/src/main/java/convex/core/data/AHashMap.java | 6 ++++++
 convex-core/src/main/java/convex/core/data/MapLeaf.java  | 5 +++++
 convex-core/src/main/java/convex/core/data/MapTree.java  | 9 +++++++++
 3 files changed, 20 insertions(+)

diff --git a/convex-core/src/main/java/convex/core/data/AHashMap.java b/convex-core/src/main/java/convex/core/data/AHashMap.java
index 4472eb928..7e71cb0f6 100644
--- a/convex-core/src/main/java/convex/core/data/AHashMap.java
+++ b/convex-core/src/main/java/convex/core/data/AHashMap.java
@@ -175,6 +175,12 @@ public AVector<K> getKeys() {
 		return Vectors.wrap(keys);
 	}
 	
+	/**
+	 * Gets the Hash for the first entry. Useful for prefix comparisons etc.
+	 * @return
+	 */
+	protected abstract Hash getFirstHash();
+	
 	@Override
 	public HashSet<Entry<K, V>> entrySet() {
 		int len = size();
diff --git a/convex-core/src/main/java/convex/core/data/MapLeaf.java b/convex-core/src/main/java/convex/core/data/MapLeaf.java
index 80917042a..b19047e7d 100644
--- a/convex-core/src/main/java/convex/core/data/MapLeaf.java
+++ b/convex-core/src/main/java/convex/core/data/MapLeaf.java
@@ -758,4 +758,9 @@ public MapLeaf<K, V> slice(long start, long end) {
 		return new MapLeaf<K,V>(nrefs);
 	}
 
+	@Override
+	protected Hash getFirstHash() {
+		return entries[0].getKeyHash();
+	}
+
 }
diff --git a/convex-core/src/main/java/convex/core/data/MapTree.java b/convex-core/src/main/java/convex/core/data/MapTree.java
index df15f3556..db3131ebf 100644
--- a/convex-core/src/main/java/convex/core/data/MapTree.java
+++ b/convex-core/src/main/java/convex/core/data/MapTree.java
@@ -933,5 +933,14 @@ public boolean isCVMValue() {
 		return true;
 	}
 
+	// Cache of first hash, we don't want to descend tree repeatedly to find this
+	private Hash firstHash;
+	
+	@Override
+	protected Hash getFirstHash() {
+		if (firstHash==null) firstHash=children[0].getValue().getFirstHash();
+		return firstHash;
+	}
+
 
 }