for _, c := range s {
		if c >= 0x80 || c == 0x00 {
			return false
		}
	}
	return true
}

// toASCII converts the input to an ASCII C-style string.
// This is a best effort conversion, so invalid characters are dropped.
func toASCII(s string) string {
	if isASCII(s) {
		return s
	}
	b := make([]byte, 0, len(s))
	for _, c := range s {
		if c < 0x80 && c != 0x00 {
			b = append(b, byte(c))
		}
	}

	MOVF.NE	(g), F3                                   // 003a9a1d
	MOVD	(g), F3                                   // 003b9aed
	MOVF	0x20(R3), F9       // MOVF 32(R3), F9     // 089a93ed
	MOVD.EQ	0x20(R4), F9       // MOVD.EQ 32(R4), F9  // 089b940d
	MOVF.NE	-0x20(g), F3       // MOVF.NE -32(g), F3  // 083a1a1d
	MOVD	-0x20(g), F3       // MOVD -32(g), F3     // 083b1aed
	MOVF	F9, (R4)                                  // 009a84ed

     * according to the XML 1.0 specification. Valid characters include:
     * - Tab (0x9)
     * - Line feed (0xA)
     * - Carriage return (0xD)
     * - Any character between 0x20 and 0xD7FF
     * - Any character between 0xE000 and 0xFFFD
     * - Any character between 0x10000 and 0x10FFFF
     *
     * @param in the input string to be processed