Implement deterministic RAND(N) and improve unseeded RAND() translation

Author: wp-fuse

wp-includes/sqlite-ast/class-wp-pdo-mysql-on-sqlite.php

@@ -4366,6 +4366,18 @@ private function translate_function_call( WP_Parser_Node $node ): string {
 		}
 
 		switch ( $name ) {
+			case 'RAND':
+				if ( empty( $args ) ) {
+					/*
+					 * SQLite's RANDOM() returns a value between -9223372036854775808 and +9223372036854775807.
+					 * We clear the sign bit (using & 0x7FFFFFFFFFFFFFFF) to get a positive integer,
+					 * then divide by 9223372036854775808.0 to get a float between 0.0 and 1.0.
+					 * We avoid ABS() because ABS(-9223372036854775808) would overflow.
+					 */
+					return '((RANDOM() & 0x7FFFFFFFFFFFFFFF) / 9223372036854775808.0)';
+				}
+				// Seeded RAND() calls should be handled by the PHP UDF.
+				return $this->translate_sequence( $node->get_children() );
 			case 'DATE_FORMAT':
 				list ( $date, $mysql_format ) = $args;
 

wp-includes/sqlite/class-wp-sqlite-pdo-user-defined-functions.php

@@ -95,6 +95,14 @@ public static function register_for( $pdo ): self {
 		'_helper_like_to_glob_pattern' => '_helper_like_to_glob_pattern',
 	);
 
+	/**
+	 * Seed instances used for the LCG pseudo-random generator (RAND).
+	 *
+	 * @var int|null
+	 */
+	private $rand_seed1 = null;
+	private $rand_seed2 = null;
+
 	/**
 	 * A helper function to throw an error from SQLite expressions.
 	 *
@@ -178,8 +186,40 @@ public function md5( $field ) {
 	 *
 	 * @return int
 	 */
-	public function rand() {
-		return mt_rand( 0, 1 );
+	public function rand( $seed = null ) {
+		$max_value = 0x3FFFFFFF; // 1073741823
+
+		if ( null !== $seed ) {
+			/*
+			 * Initialize MySQL's internal 30-bit seeds.
+			 * These constants match MySQL's my_rnd_init() implementation.
+			 */
+			$n                = (int) $seed;
+			$this->rand_seed1 = ( $n * 0x10001 + 55555555 ) % $max_value;
+			$this->rand_seed2 = ( $n * 0x10000001 ) % $max_value;
+
+			// Ensure seeds are positive.
+			if ( $this->rand_seed1 < 0 ) {
+				$this->rand_seed1 += $max_value;
+			}
+			if ( $this->rand_seed2 < 0 ) {
+				$this->rand_seed2 += $max_value;
+			}
+		}
+
+		if ( null !== $this->rand_seed1 && null !== $this->rand_seed2 ) {
+			/*
+			 * MySQL's LCG (Linear Congruential Generator) recurrence:
+			 * seed1 = (seed1 * 3 + seed2) % 0x3FFFFFFF
+			 * seed2 = (seed1 + seed2 + 33) % 0x3FFFFFFF
+			 */
+			$this->rand_seed1 = ( $this->rand_seed1 * 3 + $this->rand_seed2 ) % $max_value;
+			$this->rand_seed2 = ( $this->rand_seed1 + $this->rand_seed2 + 33 ) % $max_value;
+
+			return (float) $this->rand_seed1 / (float) $max_value;
+		}
+
+		return mt_rand( 0, mt_getrandmax() ) / mt_getrandmax();
 	}
 
 	/**