return replacementChar
}

// EncodeRune returns the UTF-16 surrogate pair r1, r2 for the given rune.
// If the rune is not a valid Unicode code point or does not need encoding,
// EncodeRune returns U+FFFD, U+FFFD.
func EncodeRune(r rune) (r1, r2 rune) {
	if r < surrSelf || r > maxRune {
		return replacementChar, replacementChar
	}
	r -= surrSelf
	return surr1 + (r>>10)&0x3ff, surr2 + r&0x3ff
}

				if r1 != rune(tt.out[j]) || r2 != rune(tt.out[j+1]) {
					t.Errorf("EncodeRune(%#x) = %#x, %#x; want %#x, %#x", r, r1, r2, tt.out[j], tt.out[j+1])
				}
				j += 2
				dec := DecodeRune(r1, r2)
				if dec != r {
					t.Errorf("DecodeRune(%#x, %#x) = %#x; want %#x", r1, r2, dec, r)
				}
			}
		}
		if j != len(tt.out) {
			t.Errorf("#%d: EncodeRune didn't generate enough output", i)
		}
	}
}

	const JamoUTF8Len = 3
	r -= hangulBase
	x := r % jamoTCount
	r /= jamoTCount
	utf8.EncodeRune(buf, jamoLBase+r/jamoVCount)
	utf8.EncodeRune(buf[JamoUTF8Len:], jamoVBase+r%jamoVCount)
	if x != 0 {
		utf8.EncodeRune(buf[2*JamoUTF8Len:], jamoTBase+x)
		return 3 * JamoUTF8Len
	}
	return 2 * JamoUTF8Len
}

// decomposeHangul algorithmically decomposes a Hangul rune into

		b := []byte(m.str)
		r, size := DecodeRune(b)
		if r != RuneError || size != 1 {
			t.Errorf("DecodeRune(%q) = %x, %d want %x, %d", b, r, size, RuneError, 1)
		}
		s := m.str
		r, size = DecodeRuneInString(s)
		if r != RuneError || size != 1 {
			t.Errorf("DecodeRuneInString(%q) = %x, %d want %x, %d", b, r, size, RuneError, 1)
		}
	}
}

// Check that DecodeRune and DecodeLastRune correspond to

	}
	var dum [4]byte
	size1 := 0
	for _, r := range a {
		size1 += encoderune(dum[:], r)
	}
	s, b := rawstringtmp(buf, size1+3)
	size2 := 0
	for _, r := range a {
		// check for race
		if size2 >= size1 {
			break
		}
		size2 += encoderune(b[size2:], r)
	}
	return s[:size2]
}

type stringStruct struct {
	str unsafe.Pointer
	len int
}

			if r > unicode.MaxRune {
				r, j = r/16, j-1
			}
			n := utf8.EncodeRune(b[len(b):cap(b)], r)
			// The optional space at the end allows a hex
			// sequence to be followed by a literal hex.
			// string(decodeCSS([]byte(`\A B`))) == "\nB"
			b, s = b[:len(b)+n], skipCSSSpace(s[j:])
		} else {
			// `\\` decodes to `\` and `\"` to `"`.
			_, n := utf8.DecodeRune(s[1:])
			b, s = append(b, s[1:1+n]...), s[1+n:]
		}
	}
	return b

	case r <= rune3Max:
		return 3
	case r <= MaxRune:
		return 4
	}
	return -1
}

// EncodeRune writes into p (which must be large enough) the UTF-8 encoding of the rune.
// If the rune is out of range, it writes the encoding of [RuneError].
// It returns the number of bytes written.
func EncodeRune(p []byte, r rune) int {
	// Negative values are erroneous. Making it unsigned addresses the problem.

					rr1 := getu4(s[r:])
					if dec := utf16.DecodeRune(rr, rr1); dec != unicode.ReplacementChar {
						// A valid pair; consume.
						r += 6
						w += utf8.EncodeRune(b[w:], dec)
						break
					}
					// Invalid surrogate; fall back to replacement rune.
					rr = unicode.ReplacementChar
				}
				w += utf8.EncodeRune(b[w:], rr)
			}

		// Quote, control characters are invalid.

func TestRuneIO(t *testing.T) {
	const NRune = 1000
	// Built a test slice while we write the data
	b := make([]byte, utf8.UTFMax*NRune)
	var buf Buffer
	n := 0
	for r := rune(0); r < NRune; r++ {
		size := utf8.EncodeRune(b[n:], r)
		nbytes, err := buf.WriteRune(r)
		if err != nil {
			t.Fatalf("WriteRune(%U) error: %s", r, err)
		}
		if nbytes != size {
			t.Fatalf("WriteRune(%U) expected %d, got %d", r, size, nbytes)
		}

func subscript(x uint64) string {
	const w = len("₀") // all digits 0...9 have the same utf8 width
	var buf [32 * w]byte
	i := len(buf)
	for {
		i -= w
		utf8.EncodeRune(buf[i:], '₀'+rune(x%10)) // '₀' == U+2080
		x /= 10
		if x == 0 {
			break
		}
	}
	return string(buf[i:])