From 4f2a8a1a07388897c0876380fe5402eeb9ed6999 Mon Sep 17 00:00:00 2001
From: Toru Maesaka <toru@chronohq.com>
Date: Thu, 3 Oct 2024 15:43:08 -0700
Subject: [PATCH] radixdb: add longestCommonPrefix()

---
 radixdb.go      | 25 +++++++++++++++++++++++++
 radixdb_test.go | 29 +++++++++++++++++++++++++++++
 2 files changed, 54 insertions(+)
 create mode 100644 radixdb_test.go

diff --git a/radixdb.go b/radixdb.go
index 38f81b8..90f61c3 100644
--- a/radixdb.go
+++ b/radixdb.go
@@ -37,3 +37,28 @@ func (rdb *RadixDB) Len() uint64 {
 
 	return rdb.numNodes
 }
+
+// longestCommonPrefix compares the two given byte slices, and returns the
+// longest common prefix. It ensures memory-safety by establishing an index
+// boundary based on the length of the shorter byte slice.
+func longestCommonPrefix(a, b []byte) []byte {
+	minLen := len(a)
+
+	if len(b) < minLen {
+		minLen = len(b)
+	}
+
+	var i int
+
+	for i = 0; i < minLen; i++ {
+		if a[i] != b[i] {
+			break
+		}
+	}
+
+	if i == 0 {
+		return nil
+	}
+
+	return a[:i]
+}
diff --git a/radixdb_test.go b/radixdb_test.go
new file mode 100644
index 0000000..0482625
--- /dev/null
+++ b/radixdb_test.go
@@ -0,0 +1,29 @@
+package radixdb
+
+import "testing"
+
+func TestLongestCommonPrefix(t *testing.T) {
+	tests := []struct {
+		a, b     []byte
+		expected []byte
+	}{
+		// Basic cases.
+		{[]byte("apple"), []byte("app"), []byte("app")},
+		{[]byte("banana"), []byte("band"), []byte("ban")},
+		{[]byte("cat"), []byte("candy"), []byte("ca")},
+		{[]byte("no"), []byte("match"), nil},
+		{[]byte("match"), []byte("match"), []byte("match")},
+
+		// Edge cases.
+		{[]byte(""), []byte(""), nil},
+		{nil, nil, nil},
+	}
+
+	for _, test := range tests {
+		subject := longestCommonPrefix(test.a, test.b)
+
+		if string(subject) != string(test.expected) {
+			t.Errorf("(%q,%q): got:%q, want:%q", test.a, test.b, subject, test.expected)
+		}
+	}
+}