From 604ce7370a68f23e372c30bd26be5264f3cc2f30 Mon Sep 17 00:00:00 2001
From: Oscar Mira <valldrac@molly.im>
Date: Wed, 21 May 2025 00:23:35 +0200
Subject: [PATCH] checkpoints: support nearest lower checkpoint lookup

(cherry picked from commit e5c424b38d51705ffd1722aa2fe3a0e7db9a40d4)
---
 src/checkpoints/checkpoints.cpp | 13 +++++++++++++
 src/checkpoints/checkpoints.h   |  8 ++++++++
 2 files changed, 21 insertions(+)

diff --git a/src/checkpoints/checkpoints.cpp b/src/checkpoints/checkpoints.cpp
index 2902bafb2..45589d985 100644
--- a/src/checkpoints/checkpoints.cpp
+++ b/src/checkpoints/checkpoints.cpp
@@ -158,6 +158,19 @@ namespace cryptonote
     return m_points.rbegin()->first;
   }
   //---------------------------------------------------------------------------
+  uint64_t checkpoints::get_nearest_checkpoint_height(uint64_t block_height) const
+  {
+    if (m_points.empty())
+      return 0;
+
+    auto it = m_points.upper_bound(block_height);
+    if (it == m_points.begin())
+      return 0;
+
+    --it;
+    return it->first;
+  }
+  //---------------------------------------------------------------------------
   const std::map<uint64_t, crypto::hash>& checkpoints::get_points() const
   {
     return m_points;
diff --git a/src/checkpoints/checkpoints.h b/src/checkpoints/checkpoints.h
index 07daeb4c0..d8de54eff 100644
--- a/src/checkpoints/checkpoints.h
+++ b/src/checkpoints/checkpoints.h
@@ -129,6 +129,14 @@ namespace cryptonote
      */
     uint64_t get_max_height() const;
 
+    /**
+     * @brief gets the highest checkpoint height less than the given block height
+     *
+     * @param block_height the reference block height
+     * @return the nearest checkpoint height below block_height, or 0 if none
+     */
+    uint64_t get_nearest_checkpoint_height(uint64_t block_height) const;
+
     /**
      * @brief gets the checkpoints container
      *