# Port Upstream PR #1027: ParsedText Word-Width Cache and Hyphenation Early Exit

## Task

Ported upstream PR #1027 (jpirnay) into the mod. The PR reduces `ParsedText::layoutAndExtractLines` CPU time by 5–9% via two independent optimizations.

## Changes Made

**`lib/Epub/Epub/ParsedText.cpp`** (single file):
1. Added `#include <cstring>` for `memcpy`/`memcmp`
2. Added 128-entry direct-mapped word-width cache in the anonymous namespace (`WordWidthCacheEntry`, FNV-1a hash, `cachedMeasureWordWidth`). 4 KB in BSS, zero heap allocation.
3. Switched `calculateWordWidths` to use `cachedMeasureWordWidth` instead of `measureWordWidth`
4. Added `lineBreakIndices.reserve(totalWordCount / 8 + 1)` in `computeLineBreaks`
5. In `hyphenateWordAtIndex`: added reusable `prefix` string buffer (avoids per-iteration `substr` allocations) and early exit `break` when prefix exceeds available width (ascending byte-offset order means all subsequent candidates will also be too wide)

**`mod/prs/MERGED.md`**: Added PR #1027 entry (TOC link + full section with context, changes, differences, discussion).

## Key Adaptation

The upstream PR targets `std::list`-based code, but our mod already uses `std::vector` (from PR #1038). List-specific optimizations (splice in `extractLine`, `std::next` vs `std::advance`, `continuesVec` pointer sync) were not applicable. Only the algorithmic improvements were ported.

## Follow-up Items

- None. Port is complete.