From edc447eb753aa9d1ca2e4d085e47aa3de9600e38 Mon Sep 17 00:00:00 2001
From: Oscar Mira <valldrac@molly.im>
Date: Wed, 21 May 2025 00:23:35 +0200
Subject: [PATCH 1/2] checkpoints: support nearest lower checkpoint lookup

---
 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 63ec6ede96..e17740cd75 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 7a93213c93..5189145f66 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
      *

From 69345dbe29bd60096d19897fc1724383e4a65a7a Mon Sep 17 00:00:00 2001
From: Oscar Mira <valldrac@molly.im>
Date: Wed, 21 May 2025 00:40:57 +0200
Subject: [PATCH 2/2] wallet2: use nearest checkpoint to allow fast_refresh on
 old accounts

---
 src/wallet/wallet2.cpp | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/src/wallet/wallet2.cpp b/src/wallet/wallet2.cpp
index 9b09d0920a..20fadc2f69 100644
--- a/src/wallet/wallet2.cpp
+++ b/src/wallet/wallet2.cpp
@@ -3790,11 +3790,11 @@ void wallet2::fast_refresh(uint64_t stop_height, uint64_t &blocks_start_height,
 {
   std::vector<crypto::hash> hashes;
 
-  const uint64_t checkpoint_height = m_checkpoints.get_max_height();
+  const uint64_t checkpoint_height = m_checkpoints.get_nearest_checkpoint_height(stop_height);
   if ((stop_height > checkpoint_height && m_blockchain.size()-1 < checkpoint_height) && !force)
   {
     // we will drop all these, so don't bother getting them
-    uint64_t missing_blocks = m_checkpoints.get_max_height() - m_blockchain.size();
+    uint64_t missing_blocks = checkpoint_height - m_blockchain.size();
     while (missing_blocks-- > 0)
       m_blockchain.push_back(crypto::null_hash); // maybe a bit suboptimal, but deque won't do huge reallocs like vector
     m_blockchain.push_back(m_checkpoints.get_points().at(checkpoint_height));