From 1dcbb03898e1a6a705a884a5ef1fc20959604e5e Mon Sep 17 00:00:00 2001
From: Alexander Danilov <adapik@yandex.ru>
Date: Sat, 25 Jul 2026 09:42:20 +0000
Subject: [PATCH] Optimize Decoder: Replace string concatenation loops with
 array/implode
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Replace inefficient string concatenation in loops with array append
and implode pattern. This changes O(n²) string operations to O(n).

- In parseBinaryIdentifier(): collect identifier octets in array
  then implode once instead of concatenating in loop
- In parseContentLength(): collect length octets in array then
  implode once instead of concatenating in loop

This optimization is especially beneficial when parsing long-form
identifiers and content lengths, which are common in X.509 and
complex ASN.1 structures.
---
 src/ASN1/Decoder/Decoder.php | 11 +++++++----
 1 file changed, 7 insertions(+), 4 deletions(-)

diff --git a/src/ASN1/Decoder/Decoder.php b/src/ASN1/Decoder/Decoder.php
index a55d1fc..73d9eed 100644
--- a/src/ASN1/Decoder/Decoder.php
+++ b/src/ASN1/Decoder/Decoder.php
@@ -189,6 +189,7 @@ protected function parseBinaryIdentifier($binaryData, &$offsetIndex)
             return $identifier;
         }
 
+        $identifierParts = [$identifier];
         while (true) {
             if (\strlen($binaryData) <= $offsetIndex) {
                 throw new ParserException(
@@ -196,8 +197,8 @@ protected function parseBinaryIdentifier($binaryData, &$offsetIndex)
                     $offsetIndex
                 );
             }
-            $nextOctet  = $binaryData[$offsetIndex++];
-            $identifier .= $nextOctet;
+            $nextOctet = $binaryData[$offsetIndex++];
+            $identifierParts[] = $nextOctet;
 
             if ((\ord($nextOctet) & 0x80) === 0) {
                 // the most significant bit is 0 to we have reached the end of the identifier
@@ -205,7 +206,7 @@ protected function parseBinaryIdentifier($binaryData, &$offsetIndex)
             }
         }
 
-        return $identifier;
+        return \implode('', $identifierParts);
     }
 
     protected function parseContentLength(&$binaryData, &$offsetIndex)
@@ -223,6 +224,7 @@ protected function parseContentLength(&$binaryData, &$offsetIndex)
         if (($firstOctet & 0x80) != 0) {
             // bit 8 is set -> this is the long form
             $nrOfLengthOctets = $firstOctet & 0x7F;
+            $octets = [$contentLengthOctets];
             for ($i = 0; $i < $nrOfLengthOctets; $i++) {
                 if (\strlen($binaryData) <= $offsetIndex) {
                     throw new ParserException(
@@ -230,8 +232,9 @@ protected function parseContentLength(&$binaryData, &$offsetIndex)
                         $offsetIndex
                     );
                 }
-                $contentLengthOctets .= $binaryData[$offsetIndex++];
+                $octets[] = $binaryData[$offsetIndex++];
             }
+            $contentLengthOctets = \implode('', $octets);
         }
 
         return $contentLengthOctets;