From 129cd2bc482fde04bf63cc18c4ab4ec1ddf4e9c0 Mon Sep 17 00:00:00 2001
From: Eunchurn Park <eunchurn.park@gmail.com>
Date: Thu, 25 Dec 2025 15:25:36 +0900
Subject: [PATCH] Optimize glyph lookup with binary search for Korean fonts

Replace linear O(n) search with binary search O(log n) for unicode
interval lookup. Korean fonts have many intervals (~30,000+ glyphs),
so this improves text rendering performance during page navigation.
---
 lib/EpdFont/EpdFont.cpp | 26 ++++++++++++++++++++------
 1 file changed, 20 insertions(+), 6 deletions(-)

diff --git a/lib/EpdFont/EpdFont.cpp b/lib/EpdFont/EpdFont.cpp
index 0f53f95..661317d 100644
--- a/lib/EpdFont/EpdFont.cpp
+++ b/lib/EpdFont/EpdFont.cpp
@@ -59,14 +59,28 @@ bool EpdFont::hasPrintableChars(const char* string) const {
 
 const EpdGlyph* EpdFont::getGlyph(const uint32_t cp) const {
   const EpdUnicodeInterval* intervals = data->intervals;
-  for (int i = 0; i < data->intervalCount; i++) {
-    const EpdUnicodeInterval* interval = &intervals[i];
-    if (cp >= interval->first && cp <= interval->last) {
+  const int count = data->intervalCount;
+
+  if (count == 0) return nullptr;
+
+  // Binary search for O(log n) lookup instead of O(n)
+  // Critical for Korean fonts with many unicode intervals
+  int left = 0;
+  int right = count - 1;
+
+  while (left <= right) {
+    const int mid = left + (right - left) / 2;
+    const EpdUnicodeInterval* interval = &intervals[mid];
+
+    if (cp < interval->first) {
+      right = mid - 1;
+    } else if (cp > interval->last) {
+      left = mid + 1;
+    } else {
+      // Found: cp >= interval->first && cp <= interval->last
       return &data->glyph[interval->offset + (cp - interval->first)];
     }
-    if (cp < interval->first) {
-      return nullptr;
-    }
   }
+
   return nullptr;
 }