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Fix/scanner quadratic scanning #1

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Merged
maxrice merged 2 commits into from
Sep 16, 2026
Merged

Fix/scanner quadratic scanning #1

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e317277
Scan in linear time instead of quadratic
maxrice Sep 16, 2026
6335f26
Cover the scanner's multibyte handling directly
maxrice Sep 16, 2026
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122 changes: 87 additions & 35 deletions src/Scanner/Scanner.php
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Original file line number Diff line number Diff line change
Expand Up @@ -13,7 +13,19 @@
*/
final class Scanner implements JsonScanner
{
private string $text;
/**
* The document split into individual characters, indexed by character offset.
*
* The scanner addresses text by character offset, not byte offset. Resolving
* such an offset against a UTF-8 string means walking it from the start, so
* doing that once per character makes scanning quadratic in the length of the
* document. Splitting once up front turns every subsequent access into an
* array lookup, at a memory cost of roughly 46x the source size.
*
* @var list<string>
*/
private array $chars;

private int $len;
private int $pos = 0;
private string $value = '';
Expand All @@ -40,12 +52,52 @@ private function __construct(
string $text,
private readonly bool $ignoreTrivia
) {
$this->text = $text;
$this->len = StringHelper::length($text);
$this->chars = mb_str_split($text, 1, 'UTF-8');
$this->len = count($this->chars);
$this->token = SyntaxKind::Unknown;
$this->scanError = ScanError::None;
}

/**
* Get the Unicode code point at a character offset, or 0 when out of bounds.
*/
private function charCodeAt(int $pos): int
{
$char = $this->chars[$pos] ?? '';

if ($char === '') {
return 0;
}

// A single-byte UTF-8 character is its own code point, which covers
// essentially all of a JSON document's structure and keys.
if (strlen($char) === 1) {
return ord($char);
}

$code = mb_ord($char, 'UTF-8');

return $code !== false ? $code : 0;
}

/**
* Get the text between two character offsets, or to the end when $end is null.
*/
private function substring(int $start, ?int $end = null): string
{
if ($end === null) {
return implode('', array_slice($this->chars, $start));
}

$length = $end - $start;

if ($length < 0) {
return '';
}

return implode('', array_slice($this->chars, $start, $length));
}

public function setPosition(int $pos): void
{
$this->pos = $pos;
Expand Down Expand Up @@ -106,7 +158,7 @@ private function scanHexDigits(int $count, bool $exact = false): int
$value = 0;

while ($digits < $count || !$exact) {
$ch = StringHelper::charCodeAt($this->text, $this->pos);
$ch = $this->charCodeAt($this->pos);

if ($ch >= CC::DIGIT_0 && $ch <= CC::DIGIT_9) {
$value = $value * 16 + $ch - CC::DIGIT_0;
Expand All @@ -133,42 +185,42 @@ private function scanNumber(): string
{
$start = $this->pos;

if (StringHelper::charCodeAt($this->text, $this->pos) === CC::DIGIT_0) {
if ($this->charCodeAt($this->pos) === CC::DIGIT_0) {
$this->pos++;
} else {
$this->pos++;
while ($this->pos < $this->len && $this->isDigit(StringHelper::charCodeAt($this->text, $this->pos))) {
while ($this->pos < $this->len && $this->isDigit($this->charCodeAt($this->pos))) {
$this->pos++;
}
}

if ($this->pos < $this->len && StringHelper::charCodeAt($this->text, $this->pos) === CC::DOT) {
if ($this->pos < $this->len && $this->charCodeAt($this->pos) === CC::DOT) {
$this->pos++;
if ($this->pos < $this->len && $this->isDigit(StringHelper::charCodeAt($this->text, $this->pos))) {
if ($this->pos < $this->len && $this->isDigit($this->charCodeAt($this->pos))) {
$this->pos++;
while ($this->pos < $this->len && $this->isDigit(StringHelper::charCodeAt($this->text, $this->pos))) {
while ($this->pos < $this->len && $this->isDigit($this->charCodeAt($this->pos))) {
$this->pos++;
}
} else {
$this->scanError = ScanError::UnexpectedEndOfNumber;
return StringHelper::substring($this->text, $start, $this->pos);
return $this->substring($start, $this->pos);
}
}

$end = $this->pos;
if ($this->pos < $this->len) {
$ch = StringHelper::charCodeAt($this->text, $this->pos);
$ch = $this->charCodeAt($this->pos);
if ($ch === CC::UPPER_E || $ch === CC::LOWER_E) {
$this->pos++;
if ($this->pos < $this->len) {
$ch = StringHelper::charCodeAt($this->text, $this->pos);
$ch = $this->charCodeAt($this->pos);
if ($ch === CC::PLUS || $ch === CC::MINUS) {
$this->pos++;
}
}
if ($this->pos < $this->len && $this->isDigit(StringHelper::charCodeAt($this->text, $this->pos))) {
if ($this->pos < $this->len && $this->isDigit($this->charCodeAt($this->pos))) {
$this->pos++;
while ($this->pos < $this->len && $this->isDigit(StringHelper::charCodeAt($this->text, $this->pos))) {
while ($this->pos < $this->len && $this->isDigit($this->charCodeAt($this->pos))) {
$this->pos++;
}
$end = $this->pos;
Expand All @@ -178,7 +230,7 @@ private function scanNumber(): string
}
}

return StringHelper::substring($this->text, $start, $end);
return $this->substring($start, $end);
}

private function scanString(): string
Expand All @@ -188,29 +240,29 @@ private function scanString(): string

while (true) {
if ($this->pos >= $this->len) {
$result .= StringHelper::substring($this->text, $start, $this->pos);
$result .= $this->substring($start, $this->pos);
$this->scanError = ScanError::UnexpectedEndOfString;
break;
}

$ch = StringHelper::charCodeAt($this->text, $this->pos);
$ch = $this->charCodeAt($this->pos);

if ($ch === CC::DOUBLE_QUOTE) {
$result .= StringHelper::substring($this->text, $start, $this->pos);
$result .= $this->substring($start, $this->pos);
$this->pos++;
break;
}

if ($ch === CC::BACKSLASH) {
$result .= StringHelper::substring($this->text, $start, $this->pos);
$result .= $this->substring($start, $this->pos);
$this->pos++;

if ($this->pos >= $this->len) {
$this->scanError = ScanError::UnexpectedEndOfString;
break;
}

$ch2 = StringHelper::charCodeAt($this->text, $this->pos++);
$ch2 = $this->charCodeAt($this->pos++);

switch ($ch2) {
case CC::DOUBLE_QUOTE:
Expand Down Expand Up @@ -255,7 +307,7 @@ private function scanString(): string

if ($ch >= 0 && $ch <= 0x1f) {
if ($this->isLineBreak($ch)) {
$result .= StringHelper::substring($this->text, $start, $this->pos);
$result .= $this->substring($start, $this->pos);
$this->scanError = ScanError::UnexpectedEndOfString;
break;
} else {
Expand Down Expand Up @@ -285,14 +337,14 @@ private function scanNext(): SyntaxKind
return $this->token = SyntaxKind::EOF;
}

$code = StringHelper::charCodeAt($this->text, $this->pos);
$code = $this->charCodeAt($this->pos);

// trivia: whitespace
if ($this->isWhiteSpace($code)) {
do {
$this->pos++;
$this->value .= StringHelper::fromCharCode($code);
$code = StringHelper::charCodeAt($this->text, $this->pos);
$code = $this->charCodeAt($this->pos);
} while ($this->isWhiteSpace($code));

return $this->token = SyntaxKind::Trivia;
Expand All @@ -302,7 +354,7 @@ private function scanNext(): SyntaxKind
if ($this->isLineBreak($code)) {
$this->pos++;
$this->value .= StringHelper::fromCharCode($code);
if ($code === CC::CARRIAGE_RETURN && StringHelper::charCodeAt($this->text, $this->pos) === CC::LINE_FEED) {
if ($code === CC::CARRIAGE_RETURN && $this->charCodeAt($this->pos) === CC::LINE_FEED) {
$this->pos++;
$this->value .= "\n";
}
Expand Down Expand Up @@ -342,31 +394,31 @@ private function scanNext(): SyntaxKind
case CC::SLASH:
$start = $this->pos;
// Single-line comment
if (StringHelper::charCodeAt($this->text, $this->pos + 1) === CC::SLASH) {
if ($this->charCodeAt($this->pos + 1) === CC::SLASH) {
$this->pos += 2;

while ($this->pos < $this->len) {
if ($this->isLineBreak(StringHelper::charCodeAt($this->text, $this->pos))) {
if ($this->isLineBreak($this->charCodeAt($this->pos))) {
break;
}
$this->pos++;
}

$this->value = StringHelper::substring($this->text, $start, $this->pos);
$this->value = $this->substring($start, $this->pos);
return $this->token = SyntaxKind::LineCommentTrivia;
}

// Multi-line comment
if (StringHelper::charCodeAt($this->text, $this->pos + 1) === CC::ASTERISK) {
if ($this->charCodeAt($this->pos + 1) === CC::ASTERISK) {
$this->pos += 2;

$safeLength = $this->len - 1; // For lookahead
$commentClosed = false;

while ($this->pos < $safeLength) {
$ch = StringHelper::charCodeAt($this->text, $this->pos);
$ch = $this->charCodeAt($this->pos);

if ($ch === CC::ASTERISK && StringHelper::charCodeAt($this->text, $this->pos + 1) === CC::SLASH) {
if ($ch === CC::ASTERISK && $this->charCodeAt($this->pos + 1) === CC::SLASH) {
$this->pos += 2;
$commentClosed = true;
break;
Expand All @@ -375,7 +427,7 @@ private function scanNext(): SyntaxKind
$this->pos++;

if ($this->isLineBreak($ch)) {
if ($ch === CC::CARRIAGE_RETURN && StringHelper::charCodeAt($this->text, $this->pos) === CC::LINE_FEED) {
if ($ch === CC::CARRIAGE_RETURN && $this->charCodeAt($this->pos) === CC::LINE_FEED) {
$this->pos++;
}
$this->lineNumber++;
Expand All @@ -388,7 +440,7 @@ private function scanNext(): SyntaxKind
$this->scanError = ScanError::UnexpectedEndOfComment;
}

$this->value = StringHelper::substring($this->text, $start, $this->pos);
$this->value = $this->substring($start, $this->pos);
return $this->token = SyntaxKind::BlockCommentTrivia;
}

Expand All @@ -401,7 +453,7 @@ private function scanNext(): SyntaxKind
case CC::MINUS:
$this->value .= StringHelper::fromCharCode($code);
$this->pos++;
if ($this->pos === $this->len || !$this->isDigit(StringHelper::charCodeAt($this->text, $this->pos))) {
if ($this->pos === $this->len || !$this->isDigit($this->charCodeAt($this->pos))) {
return $this->token = SyntaxKind::Unknown;
}
// found a minus, followed by a number so
Expand All @@ -425,11 +477,11 @@ private function scanNext(): SyntaxKind
// is a literal? Read the full word.
while ($this->pos < $this->len && $this->isUnknownContentCharacter($code)) {
$this->pos++;
$code = StringHelper::charCodeAt($this->text, $this->pos);
$code = $this->charCodeAt($this->pos);
}

if ($this->tokenOffset !== $this->pos) {
$this->value = StringHelper::substring($this->text, $this->tokenOffset, $this->pos);
$this->value = $this->substring($this->tokenOffset, $this->pos);
// keywords: true, false, null
switch ($this->value) {
case 'true':
Expand Down
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