_mb_chr( int $codepoint, "UTF-8"|null $encoding = null ): string|false

141function _mb_chr( $codepoint, $encoding = null ) {142	if ( ! is_int( $codepoint ) || ( isset( $encoding ) && 'UTF-8' !== $encoding ) ) {143		return false;144	}145 146	// Pre-check to ensure a valid code point.147	if (148		$codepoint < 0 ||149		( $codepoint >= 0xD800 && $codepoint <= 0xDFFF ) ||150		$codepoint > 0x10FFFF151	) {152		return false;153	}154 155	if ( $codepoint <= 0x7F ) {156		return chr( $codepoint );157	}158 159	if ( $codepoint <= 0x7FF ) {160		$byte1 = chr( ( $codepoint >> 6 ) | 0xC0 );161		$byte2 = chr( $codepoint & 0x3F | 0x80 );162 163		return "{$byte1}{$byte2}";164	}165 166	if ( $codepoint <= 0xFFFF ) {167		$byte1 = chr( ( $codepoint >> 12 ) | 0xE0 );168		$byte2 = chr( ( $codepoint >> 6 ) & 0x3F | 0x80 );169		$byte3 = chr( $codepoint & 0x3F | 0x80 );170 171		return "{$byte1}{$byte2}{$byte3}";172	}173 174	// Any values above U+10FFFF are eliminated above in the pre-check.175	$byte1 = chr( ( $codepoint >> 18 ) | 0xF0 );176	$byte2 = chr( ( $codepoint >> 12 ) & 0x3F | 0x80 );177	$byte3 = chr( ( $codepoint >> 6 ) & 0x3F | 0x80 );178	$byte4 = chr( $codepoint & 0x3F | 0x80 );179 180	return "{$byte1}{$byte2}{$byte3}{$byte4}";181}