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perf: read ahead optimization for OSC/DCS/APC PUT #5832

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a3dda7f
perf: unroll payload inner loops for OSC_PUT, DCS_PUT, APC_PUT
homanp Apr 23, 2026
db3119d
Merge branch 'master' into perf/payload-loop-unrolling
jerch May 10, 2026
a69072a
fix APC_PUT state
jerch May 10, 2026
a4f910d
perf: fast-path simple string payloads
homanp May 11, 2026
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20 changes: 20 additions & 0 deletions src/common/parser/EscapeSequenceParser.test.ts
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Original file line number Diff line number Diff line change
Expand Up @@ -1045,6 +1045,16 @@ describe('EscapeSequenceParser', () => {
parser.reset();
testTerminal.clear();
});
it('state DCS_PASSTHROUGH ignores DEL inside payload', () => {
parser.reset();
testTerminal.clear();
parser.currentState = ParserState.DCS_PASSTHROUGH;
parse(parser, 'abc\x7fdef');
assert.equal(parser.currentState, ParserState.DCS_PASSTHROUGH);
testTerminal.compare([['dcs put', 'abc'], ['dcs put', 'def']]);
parser.reset();
testTerminal.clear();
});
it('state APC_ENTRY', () => {
parser.reset();
// C0
Expand Down Expand Up @@ -1153,6 +1163,16 @@ describe('EscapeSequenceParser', () => {
testTerminal.clear();
}
});
it('state APC_PASSTHROUGH ignores non-payload bytes inside payload', () => {
parser.reset();
testTerminal.clear();
parser.currentState = ParserState.APC_PASSTHROUGH;
parse(parser, 'abc\x19def\x7fghi');
assert.equal(parser.currentState, ParserState.APC_PASSTHROUGH);
testTerminal.compare([['apc put', 'abc'], ['apc put', 'def'], ['apc put', 'ghi']]);
parser.reset();
testTerminal.clear();
});
it('trans APC_PASSTHROUGH --> GROUND|ESCAPE with end action', () => {
parser.reset();
testTerminal.clear();
Expand Down
203 changes: 181 additions & 22 deletions src/common/parser/EscapeSequenceParser.ts
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Original file line number Diff line number Diff line change
Expand Up @@ -539,10 +539,12 @@ export class EscapeSequenceParser extends Disposable implements IEscapeSequenceP
* - DCS_PARAM:PARAM
* - OSC_STRING:OSC_PUT
* - DCS_PASSTHROUGH:DCS_PUT
* - APC_PASSTHROUGH:APC_PUT
*
* Additionally the following fast paths exist before the table lookup:
* - EXE bytes < 0x18 in non-payload states (avoids table lookup entirely)
* - 7-bit CSI sequences without intermediates (ESC [ params final)
* - simple 7-bit string sequences (ESC ]/P/_ id payload ST)
*
* Note on asynchronous handler support:
* Any handler returning a promise will be treated as asynchronous.
Expand Down Expand Up @@ -575,6 +577,8 @@ export class EscapeSequenceParser extends Disposable implements IEscapeSequenceP
let code = 0;
let transition = 0;
let start = 0;
let c = 0;
const l4 = length - 4;
let handlerResult: void | boolean | Promise<boolean>;

// resume from async handler
Expand Down Expand Up @@ -681,7 +685,7 @@ export class EscapeSequenceParser extends Disposable implements IEscapeSequenceP
// continue with main sync loop

// process input string
for (let i = start; i < length; ++i) {
parseLoop: for (let i = start; i < length; ++i) {
code = data[i];

// EXE fast-path: common control bytes (0x00-0x17) in non-payload states
Expand Down Expand Up @@ -745,6 +749,148 @@ export class EscapeSequenceParser extends Disposable implements IEscapeSequenceP
continue;
}

// Fast-path simple OSC/DCS/APC strings; fall back on complex forms.
stringFastPath: if (code === 0x1b && this.currentState < ParserState.OSC_STRING && i + 2 < length) {
const introducer = data[i + 1];
if (introducer !== 0x50 && introducer !== 0x5d && introducer !== 0x5f) {
break stringFastPath;
}

if (introducer === 0x5d) {
let k = i + 2;
for (; k < length; k++) {
const ch = data[k];
if (ch >= 0x20 && (ch <= 0x7f || ch >= NON_ASCII_PRINTABLE)) {
continue;
}
if (ch === 0x1b && k + 1 < length && data[k + 1] === 0x5c) {
this._params.resetZdm();
this._collect = 0;
this._oscParser.start();
this._oscParser.put(data, i + 2, k);
handlerResult = this._oscParser.end(true);
if (handlerResult) {
this._preserveStack(ParserStackType.OSC, [], 0, ParserState.GROUND, k);
return handlerResult;
}
this.currentState = ParserState.GROUND;
this.precedingJoinState = 0;
i = k + 1;
continue parseLoop;
}
if (ch === 0x9c || ch === 0x07 || ch === 0x18 || ch === 0x1a) {
this._params.resetZdm();
this._collect = 0;
this._oscParser.start();
this._oscParser.put(data, i + 2, k);
handlerResult = this._oscParser.end(ch !== 0x18 && ch !== 0x1a);
if (handlerResult) {
this._preserveStack(ParserStackType.OSC, [], 0, ParserState.GROUND, k);
return handlerResult;
}
this.currentState = ParserState.GROUND;
this.precedingJoinState = 0;
i = k;
continue parseLoop;
}
break stringFastPath;
}
if (k === length) {
this._params.resetZdm();
this._collect = 0;
this._oscParser.start();
this._oscParser.put(data, i + 2, length);
this.currentState = ParserState.OSC_STRING;
i = length - 1;
continue parseLoop;
}
}

if (i + 3 >= length) {
break stringFastPath;
}

const isDcs = introducer === 0x50;
const identifier = data[i + 2];
if ((isDcs && (identifier < 0x40 || identifier > 0x7e))
|| (!isDcs && (identifier < 0x30 || identifier > 0x7e))
) {
break stringFastPath;
}

let k = i + 3;
for (; k < length; k++) {
const ch = data[k];
if (ch >= 0x20 && (ch <= 0x7e || ch >= NON_ASCII_PRINTABLE)) {
continue;
}
if (ch === 0x1b && k + 1 < length && data[k + 1] === 0x5c) {
this._params.resetZdm();
this._collect = 0;
if (isDcs) {
this._dcsParser.hook(identifier, this._params);
this._dcsParser.put(data, i + 3, k);
handlerResult = this._dcsParser.unhook(true);
if (handlerResult) {
this._preserveStack(ParserStackType.DCS, [], 0, ParserState.GROUND, k);
return handlerResult;
}
} else {
this._apcParser.start(identifier);
this._apcParser.put(data, i + 3, k);
handlerResult = this._apcParser.end(true);
if (handlerResult) {
this._preserveStack(ParserStackType.APC, [], 0, ParserState.GROUND, k);
return handlerResult;
}
}
this.currentState = ParserState.GROUND;
this.precedingJoinState = 0;
i = k + 1;
continue parseLoop;
}
if (ch === 0x9c || ch === 0x18 || ch === 0x1a) {
this._params.resetZdm();
this._collect = 0;
if (isDcs) {
this._dcsParser.hook(identifier, this._params);
this._dcsParser.put(data, i + 3, k);
handlerResult = this._dcsParser.unhook(ch !== 0x18 && ch !== 0x1a);
if (handlerResult) {
this._preserveStack(ParserStackType.DCS, [], 0, ParserState.GROUND, k);
return handlerResult;
}
} else {
this._apcParser.start(identifier);
this._apcParser.put(data, i + 3, k);
handlerResult = this._apcParser.end(ch !== 0x18 && ch !== 0x1a);
if (handlerResult) {
this._preserveStack(ParserStackType.APC, [], 0, ParserState.GROUND, k);
return handlerResult;
}
}
this.currentState = ParserState.GROUND;
this.precedingJoinState = 0;
i = k;
continue parseLoop;
}
break stringFastPath;
}
this._params.resetZdm();
this._collect = 0;
if (isDcs) {
this._dcsParser.hook(identifier, this._params);
this._dcsParser.put(data, i + 3, length);
this.currentState = ParserState.DCS_PASSTHROUGH;
} else {
this._apcParser.start(identifier);
this._apcParser.put(data, i + 3, length);
this.currentState = ParserState.APC_PASSTHROUGH;
}
i = length - 1;
continue parseLoop;
}

// normal transition & action lookup
transition = this._transitions.table[
this.currentState << TableAccess.INDEX_STATE_SHIFT |
Expand All @@ -753,8 +899,7 @@ export class EscapeSequenceParser extends Disposable implements IEscapeSequenceP
switch (transition >> TableAccess.TRANSITION_ACTION_SHIFT) {
case ParserAction.PRINT:
// Note: 0x20 (SP) is included, 0x7F (DEL) is excluded
let c = i;
const l4 = length - 4;
c = i;
while (c < l4
&& data[++c] >= 0x20 && (data[c] <= 0x7e || data[c] >= NON_ASCII_PRINTABLE)
&& data[++c] >= 0x20 && (data[c] <= 0x7e || data[c] >= NON_ASCII_PRINTABLE)
Expand Down Expand Up @@ -858,13 +1003,18 @@ export class EscapeSequenceParser extends Disposable implements IEscapeSequenceP
case ParserAction.DCS_PUT:
// inner loop - exit DCS_PUT: 0x18, 0x1a, 0x1b, 0x7f, 0x80 - 0x9f
// unhook triggered by: 0x1b, 0x9c (success) and 0x18, 0x1a (abort)
for (let j = i + 1; ; ++j) {
if (j >= length || (code = data[j]) === 0x18 || code === 0x1a || code === 0x1b || (code > 0x7f && code < NON_ASCII_PRINTABLE)) {
this._dcsParser.put(data, i, j);
i = j - 1;
break;
}
c = i;
for (; c < l4;) {
if (((code = data[++c]) <= 0x1b || code >= 0x7f) && (code === 0x1b || code === 0x1a || code === 0x18 || code === 0x7f || (code > 0x7f && code < NON_ASCII_PRINTABLE))) break;
if (((code = data[++c]) <= 0x1b || code >= 0x7f) && (code === 0x1b || code === 0x1a || code === 0x18 || code === 0x7f || (code > 0x7f && code < NON_ASCII_PRINTABLE))) break;
if (((code = data[++c]) <= 0x1b || code >= 0x7f) && (code === 0x1b || code === 0x1a || code === 0x18 || code === 0x7f || (code > 0x7f && code < NON_ASCII_PRINTABLE))) break;
if (((code = data[++c]) <= 0x1b || code >= 0x7f) && (code === 0x1b || code === 0x1a || code === 0x18 || code === 0x7f || (code > 0x7f && code < NON_ASCII_PRINTABLE))) break;
}
if (c >= l4) {
while (c < length && !(((code = data[c]) <= 0x1b || code >= 0x7f) && (code === 0x1b || code === 0x1a || code === 0x18 || code === 0x7f || (code > 0x7f && code < NON_ASCII_PRINTABLE)))) c++;
}
this._dcsParser.put(data, i, c);
i = c - 1;
break;
case ParserAction.DCS_UNHOOK:
handlerResult = this._dcsParser.unhook(code !== 0x18 && code !== 0x1a);
Expand All @@ -882,13 +1032,18 @@ export class EscapeSequenceParser extends Disposable implements IEscapeSequenceP
break;
case ParserAction.OSC_PUT:
// inner loop: 0x20 (SP) included, 0x7F (DEL) included
for (let j = i + 1; ; j++) {
if (j >= length || (code = data[j]) < 0x20 || (code > 0x7f && code < NON_ASCII_PRINTABLE)) {
this._oscParser.put(data, i, j);
i = j - 1;
break;
}
c = i;
while (c < l4
&& data[++c] >= 0x20 && (data[c] <= 0x7f || data[c] >= NON_ASCII_PRINTABLE)
&& data[++c] >= 0x20 && (data[c] <= 0x7f || data[c] >= NON_ASCII_PRINTABLE)
&& data[++c] >= 0x20 && (data[c] <= 0x7f || data[c] >= NON_ASCII_PRINTABLE)
&& data[++c] >= 0x20 && (data[c] <= 0x7f || data[c] >= NON_ASCII_PRINTABLE)
) {}
if (c >= l4) {
while (c < length && data[c] >= 0x20 && (data[c] <= 0x7f || data[c] >= NON_ASCII_PRINTABLE)) c++;
}
this._oscParser.put(data, i, c);
i = c - 1;
break;
case ParserAction.OSC_END:
handlerResult = this._oscParser.end(code !== 0x18 && code !== 0x1a);
Expand All @@ -907,14 +1062,18 @@ export class EscapeSequenceParser extends Disposable implements IEscapeSequenceP
case ParserAction.APC_PUT:
// inner loop - exit APC_PUT: 0x18, 0x1a, 0x1b, 0x9c
// allowed: 00/08 .. 00/13, 02/00 .. 07/14 + NON_ASCII_PRINTABLE
for (let j = i + 1; ; ++j) {
if (j < length && (
(data[j] >= 0x20 && data[j] < 0x7f) || (data[j] >= 0x08 && data[j] < 0x0e) || data[j] >= NON_ASCII_PRINTABLE
)) continue;
this._apcParser.put(data, i, j);
i = j - 1;
break;
c = i;
for (; c < l4;) {
if (((code = data[++c]) < 0x20 || code >= 0x7f) && (code < 0x08 || (code >= 0x0e && code < 0x20) || (code >= 0x7f && code < NON_ASCII_PRINTABLE))) break;
if (((code = data[++c]) < 0x20 || code >= 0x7f) && (code < 0x08 || (code >= 0x0e && code < 0x20) || (code >= 0x7f && code < NON_ASCII_PRINTABLE))) break;
if (((code = data[++c]) < 0x20 || code >= 0x7f) && (code < 0x08 || (code >= 0x0e && code < 0x20) || (code >= 0x7f && code < NON_ASCII_PRINTABLE))) break;
if (((code = data[++c]) < 0x20 || code >= 0x7f) && (code < 0x08 || (code >= 0x0e && code < 0x20) || (code >= 0x7f && code < NON_ASCII_PRINTABLE))) break;
}
if (c >= l4) {
while (c < length && !(((code = data[c]) < 0x20 || code >= 0x7f) && (code < 0x08 || (code >= 0x0e && code < 0x20) || (code >= 0x7f && code < NON_ASCII_PRINTABLE)))) c++;
}
this._apcParser.put(data, i, c);
i = c - 1;
break;
case ParserAction.APC_END:
handlerResult = this._apcParser.end(code !== 0x18 && code !== 0x1a);
Expand Down
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