// Use the exponent to extract the 3 appropriate uint64 digits from mPi,
	// B ~ (z0, z1, z2), such that the product leading digit has the exponent -64.
	// Note, exp >= 50 since x >= reduceThreshold and exp < 971 for maximum float64.
	digit, bitshift := uint(exp+64)/64, uint(exp+64)%64
	z0 := (mPi[digit] << bitshift) | (mPi[digit+1] >> (64 - bitshift))
	z1 := (mPi[digit+1] << bitshift) | (mPi[digit+2] >> (64 - bitshift))

	z = z.make(m + 1)
	var c big.Word
	for i := 0; i < n; i++ {
		// lower half-digit
		c += x[i]&M2 + y[i]&M2
		d := c & M2
		c >>= W2
		// upper half-digit
		c += x[i]>>W2 + y[i]>>W2
		z[i] = c<<W2 | d
		c >>= W2
	}
	for i := n; i < m; i++ {
		// lower half-digit
		c += x[i] & M2
		d := c & M2
		c >>= W2
		// upper half-digit
		c += x[i] >> W2
		z[i] = c<<W2 | d
		c >>= W2
	}
	if c != 0 {

	// Scan right to left turning 9s to 0s until you find a digit to increment.
	digits := []byte(decimal)
	i := len(digits) - 1
	for ; i >= 0 && digits[i] == '9'; i-- {
		digits[i] = '0'
	}
	if i >= 0 {
		digits[i]++
	} else {
		// digits is all zeros
		digits[0] = '1'
		digits = append(digits, '0')
	}
	return string(digits)
}

     * <p>
     * Each of the digits is the sum of its component bits in the binary numeral system.
     * Each of the 3 bits represents a permission.
     * 1st bit is the READ bit, adds 4 to the digit (binary 100).
     * 2nd bit is the WRITE bit, adds 2 to the digit (binary 010).
     * 3rd bit is the EXECUTE bit, adds 1 to the digit (binary 001).
     * <p>
     * See the examples below.
     * <p>

	var right int // space characters to right of digits for left justification ("%-8d")

	// determine number padding from precision: the least number of digits to output
	precision, precisionSet := s.Precision()
	if precisionSet {
		switch {
		case len(digits) < precision:
			zeros = precision - len(digits) // count of zero padding
		case len(digits) == 1 && digits[0] == '0' && precision == 0:

		}
		rst.advance(1)
		if val == 0 && digit == 0 && (len(rst.str) == 0 || rst.str[0] != '_') {
			rst.fail("invalid leading 0 in constant")
		}
		val *= 16
		val += digit
		digits++
	}

	if digits == 0 {
		rst.fail("expected constant")
	}

	switch kind {
	case signedInt, unsignedInt:
		if digits > 16 {
			// Value too big, just write out the string.

func (s *ss) getBase(verb rune) (base int, digits string) {
	s.okVerb(verb, "bdoUxXv", "integer") // sets s.err
	base = 10
	digits = decimalDigits
	switch verb {
	case 'b':
		base = 2
		digits = binaryDigits
	case 'o':
		base = 8
		digits = octalDigits
	case 'x', 'X', 'U':
		base = 16
		digits = hexadecimalDigits
	}
	return
}

	// Similarly to the single variable-base approach, we compute
	// digits and use them with a lookup table.  However, because
	// we are allowed to do variable-time operations, we don't
	// need constant-time lookups or constant-time digit
	// computations.
	//
	// So we use a non-adjacent form of some width w instead of
	// radix 16.  This is like a binary representation (one digit
	// for each binary place) but we allow the digits to grow in

	checkLinkOutput("0x", "usage")
	checkLinkOutput("0x0", "-B argument must have even number of digits")
	checkLinkOutput("0x00", "usage")
	checkLinkOutput("0xYZ", "-B argument contains invalid hex digit")
	checkLinkOutput("0x"+strings.Repeat("00", 32), "usage")
	checkLinkOutput("0x"+strings.Repeat("00", 33), "-B option too long (max 32 digits)")
}

func checkLinkOutput(buildid string, message string) {

	`[:space:]`:   {+1, code14},
	`[:^space:]`:  {-1, code14},
	`[:upper:]`:   {+1, code15},
	`[:^upper:]`:  {-1, code15},
	`[:word:]`:    {+1, code16},
	`[:^word:]`:   {-1, code16},
	`[:xdigit:]`:  {+1, code17},
	`[:^xdigit:]`: {-1, code17},