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fix: move CSI fast-path into CLEAR action to eliminate non-CSI regression

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The CSI fast-path check previously ran on every byte of input, causing
3-18% regressions on ESCAPE, OSC, DCS, and other non-CSI sequences.
Moving the check into the CLEAR action handler means it only evaluates
after the state machine already identified an ESC byte. The fast-path
body is extracted into a separate _csiFast method to keep the switch
case body small for V8 optimization.

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>
This commit is contained in:
Ismail Pelaseyed
2026-04-21 11:19:32 +02:00
co-authored by Claude Opus 4.6
parent 487b27f512
commit ba7e775a17
1 changed files with 65 additions and 63 deletions
Download Patch File Download Diff File Expand all files Collapse all files
src/common/parser/EscapeSequenceParser.ts
+65 -63
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@@ -492,6 +492,59 @@ export class EscapeSequenceParser extends Disposable implements IEscapeSequenceP
this._parseStack.chunkPos = chunkPos;
}
/**
* CSI fast path: scan params and dispatch from position `start` (first byte after '[').
* Returns new `i` position (>= 0) on success, -1 on failure/incomplete.
* Stores a Promise in `_parseStack` and returns -2 for async handlers.
*/
private _csiFast(data: Uint32Array, start: number, length: number): number | Promise<boolean> {
let k = start;
let ch = data[k];
if (ch >= 0x3c && ch <= 0x3f) {
this._collect = ch;
k++;
}
for (; k < length; k++) {
ch = data[k];
if (ch >= 0x30 && ch <= 0x39) {
this._params.addDigit(ch - 48);
} else if (ch === 0x3b) {
this._params.addParam(0);
} else if (ch === 0x3a) {
this._params.addSubParam(-1);
} else if (ch >= 0x40 && ch <= 0x7e) {
const handlers = this._csiHandlers[this._collect << 8 | ch];
let j = handlers ? handlers.length - 1 : -1;
for (; j >= 0; j--) {
const handlerResult = handlers[j](this._params);
if (handlerResult === true) {
break;
} else if (handlerResult instanceof Promise) {
const transition = ParserAction.CSI_DISPATCH << TableAccess.TRANSITION_ACTION_SHIFT | ParserState.GROUND;
this._preserveStack(ParserStackType.CSI, handlers, j, transition, k);
return handlerResult;
}
}
if (j < 0) {
this._csiHandlerFb(this._collect << 8 | ch, this._params);
}
this.precedingJoinState = 0;
let pEnd = k + 1;
if (pEnd < length && data[pEnd] >= 0x20 && data[pEnd] <= 0x7e) {
for (++pEnd; pEnd < length; ++pEnd) {
const pc = data[pEnd];
if (pc < 0x20 || (pc > 0x7e && pc < NON_ASCII_PRINTABLE)) break;
}
this._printHandler(data, k + 1, pEnd);
}
return pEnd - 1;
} else {
break;
}
}
return -1;
}
/**
* Parse UTF32 codepoints in `data` up to `length`.
*
@@ -649,69 +702,6 @@ export class EscapeSequenceParser extends Disposable implements IEscapeSequenceP
for (let i = start; i < length; ++i) {
code = data[i];
// CSI fast path: in GROUND seeing ESC [, consume entire CSI sequence without table lookups
if (code === 0x1b && this.currentState === ParserState.GROUND && i + 2 < length && data[i + 1] === 0x5b) {
this._params.reset();
this._params.addParam(0);
this._collect = 0;
let k = i + 2;
let ch = data[k];
if (ch >= 0x3c && ch <= 0x3f) {
this._collect = ch;
k++;
}
let csiComplete = false;
for (; k < length; k++) {
ch = data[k];
if (ch >= 0x30 && ch <= 0x39) {
this._params.addDigit(ch - 48);
} else if (ch === 0x3b) {
this._params.addParam(0);
} else if (ch === 0x3a) {
this._params.addSubParam(-1);
} else if (ch >= 0x40 && ch <= 0x7e) {
const handlers = this._csiHandlers[this._collect << 8 | ch];
let j = handlers ? handlers.length - 1 : -1;
for (; j >= 0; j--) {
handlerResult = handlers[j](this._params);
if (handlerResult === true) {
break;
} else if (handlerResult instanceof Promise) {
transition = ParserAction.CSI_DISPATCH << TableAccess.TRANSITION_ACTION_SHIFT | ParserState.GROUND;
this._preserveStack(ParserStackType.CSI, handlers, j, transition, k);
return handlerResult;
}
}
if (j < 0) {
this._csiHandlerFb(this._collect << 8 | ch, this._params);
}
this.precedingJoinState = 0;
// scan ahead for print run after CSI dispatch
let pEnd = k + 1;
if (pEnd < length && data[pEnd] >= 0x20 && data[pEnd] <= 0x7e) {
for (++pEnd; pEnd < length; ++pEnd) {
const pc = data[pEnd];
if (pc < 0x20 || (pc > 0x7e && pc < NON_ASCII_PRINTABLE)) break;
}
this._printHandler(data, k + 1, pEnd);
}
i = pEnd - 1;
csiComplete = true;
break;
} else {
break;
}
}
if (csiComplete) continue;
// incomplete or unexpected byte — fall back to normal path
this._params.reset();
this._params.addParam(0);
this._collect = 0;
this.currentState = ParserState.ESCAPE;
// let normal loop process '[' at i+1
continue;
}
// normal transition & action lookup
transition = this._transitions.table[this.currentState << TableAccess.INDEX_STATE_SHIFT | (code < 0xa0 ? code : NON_ASCII_PRINTABLE)];
switch (transition >> TableAccess.TRANSITION_ACTION_SHIFT) {
@@ -824,6 +814,18 @@ export class EscapeSequenceParser extends Disposable implements IEscapeSequenceP
this._params.reset();
this._params.addParam(0); // ZDM
this._collect = 0;
if ((transition & TableAccess.TRANSITION_STATE_MASK) === ParserState.ESCAPE
&& i + 2 < length && data[i + 1] === 0x5b) {
const csiFastResult = this._csiFast(data, i + 2, length);
if (csiFastResult instanceof Promise) {
return csiFastResult;
}
if (csiFastResult >= 0) {
i = csiFastResult as number;
this.currentState = ParserState.GROUND;
continue;
}
}
break;
case ParserAction.DCS_HOOK:
this._dcsParser.hook(this._collect << 8 | code, this._params);