//	             ::= cv <type> _ <expression>* E
//	             ::= tl <type> <braced-expression>* E
//	             ::= il <braced-expression>* E
//	             ::= [gs] nw <expression>* _ <type> E
//	             ::= [gs] nw <expression>* _ <type> <initializer>
//	             ::= [gs] na <expression>* _ <type> E
//	             ::= [gs] na <expression>* _ <type> <initializer>
//	             ::= [gs] dl <expression>

// tail of buf, omitting trailing zeros. It omits the decimal
// point too when the fraction is 0. It returns the index where the
// output bytes begin and the value v/10**prec.
func fmtFrac(buf []byte, v uint64, prec int) (nw int, nv uint64) {
	// Omit trailing zeros up to and including decimal point.
	w := len(buf)
	print := false
	for i := 0; i < prec; i++ {
		digit := v % 10
		print = print || digit != 0
		if print {
			w--