From eb65910c1ba26733cf4cef4ef9157927b08826b8 Mon Sep 17 00:00:00 2001
From: Ismail Pelaseyed <homanp@gmail.com>
Date: Thu, 23 Apr 2026 15:35:06 +0200
Subject: [PATCH] perf: simplify CSI fast-path - drop intermediate handling and
 extra length checks

Remove intermediate byte handling from the fast-path, bail to table
lookup instead. Remove redundant per-step length checks by requiring
i + 2 < length upfront and letting the for-loop guard the rest.
---
 src/common/parser/EscapeSequenceParser.ts | 12 ++----------
 1 file changed, 2 insertions(+), 10 deletions(-)

diff --git a/src/common/parser/EscapeSequenceParser.ts b/src/common/parser/EscapeSequenceParser.ts
index 04f5e8862..99770b092 100644
--- a/src/common/parser/EscapeSequenceParser.ts
+++ b/src/common/parser/EscapeSequenceParser.ts
@@ -660,17 +660,16 @@ export class EscapeSequenceParser extends Disposable implements IEscapeSequenceP
       // CSI fast-path: collapse ESC [ into a single entry, parse params+final in a tight loop
       if (code === 0x1b
         && this.currentState < ParserState.OSC_STRING
-        && i + 1 < length && data[i + 1] === 0x5b
+        && i + 2 < length && data[i + 1] === 0x5b
       ) {
         this._params.reset();
         this._params.addParam(0); // ZDM
         this._collect = 0;
         let k = i + 2;
-        if (k >= length) { i = k - 1; this.currentState = ParserState.CSI_ENTRY; continue; }
         let ch = data[k];
         if (ch >= 0x3c && ch <= 0x3f) {
           this._collect = ch;
-          if (++k >= length) { i = k - 1; this.currentState = ParserState.CSI_PARAM; continue; }
+          k++;
         }
         let csiDone = false;
         for (; k < length; k++) {
@@ -702,13 +701,6 @@ export class EscapeSequenceParser extends Disposable implements IEscapeSequenceP
             this.currentState = ParserState.GROUND;
             csiDone = true;
             break;
-          } else if (ch >= 0x20 && ch <= 0x2f) {
-            this._collect <<= 8;
-            this._collect |= ch;
-            i = k;
-            this.currentState = ParserState.CSI_INTERMEDIATE;
-            csiDone = true;
-            break;
           } else {
             break;
           }