int expectedLength = 0;
        for (String word : words) {
            if (word != null) {
                expectedLength += word.length();
            }
        }
        StringBuilder builder = new StringBuilder(expectedLength);
        for (String word : words) {
            if (word == null || word.length() == 0) {
                continue;
            }

	}
}

// TODO(gri) mulAddVWW and divWVW are symmetric operations but
// their signature is not symmetric. Try to unify.

type funWVW func(z []Word, xn Word, x []Word, y Word) (r Word)
type argWVW struct {
	z  nat
	xn Word
	x  nat
	y  Word
	r  Word
}

func testFunWVW(t *testing.T, msg string, f funWVW, a argWVW) {
	z := make(nat, len(a.z))
	r := f(z, a.xn, a.x, a.y)
	for i, zi := range z {

	"VUPLHF",
	"VUPLL",
	"VUPLLB",
	"VUPLLH",
	"VUPLLF",
	"VUPL",
	"VUPLB",
	"VUPLHW",
	"VUPLF",
	"VMSLG",
	"VMSLEG",
	"VMSLOG",
	"VMSLEOG",
	"NOPH",
	"BYTE",
	"WORD",
	"DWORD",
	"BRRK",
	"LAST",

//go:build !math_big_pure_go

package big

import "internal/cpu"

func addVV_check(z, x, y []Word) (c Word)
func addVV_vec(z, x, y []Word) (c Word)
func addVV_novec(z, x, y []Word) (c Word)
func subVV_check(z, x, y []Word) (c Word)
func subVV_vec(z, x, y []Word) (c Word)
func subVV_novec(z, x, y []Word) (c Word)

	RET


// func shrVU(z, x []Word, s uint) (c Word)
TEXT ·shrVU(SB),NOSPLIT,$0
	MOVW	z_len+4(FP), R5
	TEQ	$0, R5
	BEQ	X6

	MOVW	z+0(FP), R1
	MOVW	x+12(FP), R2
	ADD	R5<<2, R1, R5
	MOVW	s+24(FP), R3
	TEQ	$0, R3	// shift 0 is special
	BEQ Y6
	SUB	$4, R5	// stop one word early
	MOVW	$32, R4
	SUB	R3, R4
	MOVW	$0, R7

	// first word
	MOVW.P	4(R2), R6
	MOVW	R6>>R3, R7

  }

  abstract String normalizeWord(String word);

  String normalizeFirstWord(String word) {
    return normalizeWord(word);
  }

  private static String firstCharOnlyToUpper(String word) {
    return word.isEmpty()
        ? word
        : Ascii.toUpperCase(word.charAt(0)) + Ascii.toLowerCase(word.substring(1));
  }

// z1<<_W + z0 = x*y
func mulWW(x, y Word) (z1, z0 Word) {
	hi, lo := bits.Mul(uint(x), uint(y))
	return Word(hi), Word(lo)
}

// z1<<_W + z0 = x*y + c
func mulAddWWW_g(x, y, c Word) (z1, z0 Word) {
	hi, lo := bits.Mul(uint(x), uint(y))
	var cc uint
	lo, cc = bits.Add(lo, uint(c), 0)
	return Word(hi + cc), Word(lo)
}

// nlz returns the number of leading zeros in x.

//go:linkname addVW
//go:noescape
func addVW(z, x []Word, y Word) (c Word)

// subVW should be an internal detail,
// but widely used packages access it using linkname.
// Notable members of the hall of shame include:
//   - github.com/remyoudompheng/bigfft
//
// Do not remove or change the type signature.
// See go.dev/issue/67401.
//
//go:linkname subVW
//go:noescape
func subVW(z, x []Word, y Word) (c Word)

}

// Decode decodes an RFC 2047 encoded-word.
func (d *WordDecoder) Decode(word string) (string, error) {
	// See https://tools.ietf.org/html/rfc2047#section-2 for details.
	// Our decoder is permissive, we accept empty encoded-text.
	if len(word) < 8 || !strings.HasPrefix(word, "=?") || !strings.HasSuffix(word, "?=") || strings.Count(word, "?") != 4 {
		return "", errInvalidWord
	}
	word = word[2 : len(word)-2]

  }

  abstract String normalizeWord(String word);

  String normalizeFirstWord(String word) {
    return normalizeWord(word);
  }

  private static String firstCharOnlyToUpper(String word) {
    return word.isEmpty()
        ? word
        : Ascii.toUpperCase(word.charAt(0)) + Ascii.toLowerCase(word.substring(1));
  }