From 35d2d09c398e17c87ed93810b675a2efb92d4db2 Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?J=C3=A9r=C3=B4me=20Tamarelle?= <jerome@tamarelle.net>
Date: Wed, 13 May 2026 23:44:33 +0200
Subject: [PATCH 1/2] Two micro-optimizations: cache active block parser, ASCII
 fast path in isLetter
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Cache the active block parser to avoid calling end() on the parsers array
on every getActiveBlockParser() call. end() costs ~67ns; a direct property
read costs ~28ns. getActiveBlockParser() is called ~5x per line so this
compounds quickly. The cache is kept in sync in activateBlockParser() and
deactivateBlockParser().

Add an ASCII fast path to RegexHelper::isLetter(). The previous
implementation called preg_match('/[\pL]/u', $char) on every non-blank,
non-indented line to detect whether to skip block-start parsing. For
single-byte ASCII characters (the vast majority in Markdown), a direct
range comparison is ~60% faster than the regex.

Micro-benchmarks (PHP 8.5.2, OPcache on, Xdebug off):
  end($parsers)              67 ns  →  property read    28 ns  (-58%)
  preg_match Unicode         45 ns  →  char range       18 ns  (-60%)
---
 src/Parser/MarkdownParser.php | 16 ++++++++++------
 src/Util/RegexHelper.php      |  7 ++++++-
 2 files changed, 16 insertions(+), 7 deletions(-)

diff --git a/src/Parser/MarkdownParser.php b/src/Parser/MarkdownParser.php
index 904c7c45b4..75d384d0fd 100644
--- a/src/Parser/MarkdownParser.php
+++ b/src/Parser/MarkdownParser.php
@@ -53,6 +53,9 @@ final class MarkdownParser implements MarkdownParserInterface
     /** @psalm-readonly-allow-private-mutation */
     private Cursor $cursor;
 
+    /** @psalm-readonly-allow-private-mutation */
+    private BlockContinueParserInterface $activeBlockParser;
+
     /**
      * @var array<int, BlockContinueParserInterface>
      *
@@ -297,6 +300,7 @@ private function addChild(BlockContinueParserInterface $blockParser, ?int $start
     private function activateBlockParser(BlockContinueParserInterface $blockParser): void
     {
         $this->activeBlockParsers[] = $blockParser;
+        $this->activeBlockParser    = $blockParser;
     }
 
     /**
@@ -309,6 +313,11 @@ private function deactivateBlockParser(): BlockContinueParserInterface
             throw new ParserLogicException('The last block parser should not be deactivated');
         }
 
+        $last = \end($this->activeBlockParsers);
+        if ($last !== false) {
+            $this->activeBlockParser = $last;
+        }
+
         return $popped;
     }
 
@@ -346,11 +355,6 @@ private function updateReferenceMap(iterable $references): void
      */
     public function getActiveBlockParser(): BlockContinueParserInterface
     {
-        $active = \end($this->activeBlockParsers);
-        if ($active === false) {
-            throw new ParserLogicException('No active block parsers are available');
-        }
-
-        return $active;
+        return $this->activeBlockParser;
     }
 }
diff --git a/src/Util/RegexHelper.php b/src/Util/RegexHelper.php
index 429b2d85f0..38ac8b441d 100644
--- a/src/Util/RegexHelper.php
+++ b/src/Util/RegexHelper.php
@@ -98,7 +98,12 @@ public static function isLetter(?string $character): bool
             return false;
         }
 
-        return \preg_match('/[\pL]/u', $character) === 1;
+        // Fast path for ASCII letters (the common case in Markdown)
+        if (\strlen($character) === 1) {
+            return ($character >= 'a' && $character <= 'z') || ($character >= 'A' && $character <= 'Z');
+        }
+
+        return \preg_match('/^\pL/u', $character) === 1;
     }
 
     /**

From 9d945ee15bd5e974f5a0ee1a78580b1d711ebab7 Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?J=C3=A9r=C3=B4me=20Tamarelle?= <jerome@tamarelle.net>
Date: Thu, 14 May 2026 00:05:01 +0200
Subject: [PATCH 2/2] Use ctype_alpha for ASCII fast path in
 RegexHelper::isLetter()

---
 src/Util/RegexHelper.php | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/src/Util/RegexHelper.php b/src/Util/RegexHelper.php
index 38ac8b441d..e311ccdfcc 100644
--- a/src/Util/RegexHelper.php
+++ b/src/Util/RegexHelper.php
@@ -98,9 +98,9 @@ public static function isLetter(?string $character): bool
             return false;
         }
 
-        // Fast path for ASCII letters (the common case in Markdown)
+        // Fast path for ASCII (the common case in Markdown); ctype_alpha is locale-independent for single bytes
         if (\strlen($character) === 1) {
-            return ($character >= 'a' && $character <= 'z') || ($character >= 'A' && $character <= 'Z');
+            return \ctype_alpha($character);
         }
 
         return \preg_match('/^\pL/u', $character) === 1;