_wp_utf8_encode_fallback()

_wp_utf8_encode_fallback( string $iso_8859_1_text ): string

function _wp_utf8_encode_fallback( $iso_8859_1_text ) {
	$iso_8859_1_text = (string) $iso_8859_1_text;
	$at              = 0;
	$was_at          = 0;
	$end             = strlen( $iso_8859_1_text );
	$utf8            = '';

	while ( $at < $end ) {
		// US-ASCII bytes are identical in ISO-8859-1 and UTF-8. These are x00–x7F.
		$ascii_byte_count = strspn(
			$iso_8859_1_text,
			"\x00\x01\x02\x03\x04\x05\x06\x07\x08\x09\x0a\x0b\x0c\x0d\x0e\x0f" .
			"\x10\x11\x12\x13\x14\x15\x16\x17\x18\x19\x1a\x1b\x1c\x1d\x1e\x1f" .
			" !\"#$%&'()*+,-./0123456789:;<=>?@ABCDEFGHIJKLMNOPQRSTUVWXYZ[\\]^_`abcdefghijklmnopqrstuvwxyz{|}~\x7f",
			$at
		);

		if ( $ascii_byte_count > 0 ) {
			$at += $ascii_byte_count;
			continue;
		}

		// All other bytes transform into two-byte UTF-8 sequences.
		$code_point = ord( $iso_8859_1_text[ $at ] );
		$byte1      = chr( xC0 | ( $code_point >> 6 ) );
		$byte2      = chr( x80 | ( $code_point & x3F ) );

		$utf8 .= substr( $iso_8859_1_text, $was_at, $at - $was_at );
		$utf8 .= "{$byte1}{$byte2}";

		++$at;
		$was_at = $at;
	}

	if ( 0 === $was_at ) {
		return $iso_8859_1_text;
	}

	$utf8 .= substr( $iso_8859_1_text, $was_at );
	return $utf8;
}