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Optimize glyph lookup with binary search (#125)

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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.

## Summary

* **What is the goal of this PR?** (e.g., Fixes a bug in the user
authentication module, Implements the new feature for
  file uploading.)

Replace linear `O(n)` glyph lookup with binary search `O(log n)` to
improve text rendering performance during page navigation.

* **What changes are included?**

- Modified `EpdFont::getGlyph()` to use binary search instead of linear
search for unicode interval lookup
- Added early return for empty interval count

## Additional Context

* Add any other information that might be helpful for the reviewer
(e.g., performance implications, potential risks, specific areas to
focus on).

- Performance implications: Fonts with many unicode intervals benefit
the most. Korean fonts have ~30,000+ glyphs across multiple intervals,
but any font with significant glyph coverage (CJK, extended Latin,
emoji, etc.) will see improvement.
- Complexity: from `O(n)` to `O(log n)` where n = number of unicode
intervals. For fonts with 10+ intervals, this reduces lookup iterations
significantly.
- Risk: Low - the binary search logic is straightforward and the
intervals are already sorted by unicode codepoint (required for the
original early-exit optimization).
This commit is contained in:
Eunchurn Park 2025-12-26 09:46:17 +09:00 committed by GitHub
parent 504c7b307d
commit dc7544d944
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GPG Key ID: B5690EEEBB952194
1 changed files with 20 additions and 6 deletions
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26
lib/EpdFont/EpdFont.cpp
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@ -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;
}