1 files changed, 445 insertions, 0 deletions
diff --git a/src/unicode/utf8/utf8.go b/src/unicode/utf8/utf8.go
new file mode 100644
index 000000000..9ac37184d
--- /dev/null
+++ b/src/unicode/utf8/utf8.go
@@ -0,0 +1,445 @@
+// Copyright 2009 The Go Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+// Package utf8 implements functions and constants to support text encoded in
+// UTF-8. It includes functions to translate between runes and UTF-8 byte sequences.
+package utf8
+
+// The conditions RuneError==unicode.ReplacementChar and
+// MaxRune==unicode.MaxRune are verified in the tests.
+// Defining them locally avoids this package depending on package unicode.
+
+// Numbers fundamental to the encoding.
+const (
+	RuneError = '\uFFFD'     // the "error" Rune or "Unicode replacement character"
+	RuneSelf  = 0x80         // characters below Runeself are represented as themselves in a single byte.
+	MaxRune   = '\U0010FFFF' // Maximum valid Unicode code point.
+	UTFMax    = 4            // maximum number of bytes of a UTF-8 encoded Unicode character.
+)
+
+// Code points in the surrogate range are not valid for UTF-8.
+const (
+	surrogateMin = 0xD800
+	surrogateMax = 0xDFFF
+)
+
+const (
+	t1 = 0x00 // 0000 0000
+	tx = 0x80 // 1000 0000
+	t2 = 0xC0 // 1100 0000
+	t3 = 0xE0 // 1110 0000
+	t4 = 0xF0 // 1111 0000
+	t5 = 0xF8 // 1111 1000
+
+	maskx = 0x3F // 0011 1111
+	mask2 = 0x1F // 0001 1111
+	mask3 = 0x0F // 0000 1111
+	mask4 = 0x07 // 0000 0111
+
+	rune1Max = 1<<7 - 1
+	rune2Max = 1<<11 - 1
+	rune3Max = 1<<16 - 1
+)
+
+func decodeRuneInternal(p []byte) (r rune, size int, short bool) {
+	n := len(p)
+	if n < 1 {
+		return RuneError, 0, true
+	}
+	c0 := p[0]
+
+	// 1-byte, 7-bit sequence?
+	if c0 < tx {
+		return rune(c0), 1, false
+	}
+
+	// unexpected continuation byte?
+	if c0 < t2 {
+		return RuneError, 1, false
+	}
+
+	// need first continuation byte
+	if n < 2 {
+		return RuneError, 1, true
+	}
+	c1 := p[1]
+	if c1 < tx || t2 <= c1 {
+		return RuneError, 1, false
+	}
+
+	// 2-byte, 11-bit sequence?
+	if c0 < t3 {
+		r = rune(c0&mask2)<<6 | rune(c1&maskx)
+		if r <= rune1Max {
+			return RuneError, 1, false
+		}
+		return r, 2, false
+	}
+
+	// need second continuation byte
+	if n < 3 {
+		return RuneError, 1, true
+	}
+	c2 := p[2]
+	if c2 < tx || t2 <= c2 {
+		return RuneError, 1, false
+	}
+
+	// 3-byte, 16-bit sequence?
+	if c0 < t4 {
+		r = rune(c0&mask3)<<12 | rune(c1&maskx)<<6 | rune(c2&maskx)
+		if r <= rune2Max {
+			return RuneError, 1, false
+		}
+		if surrogateMin <= r && r <= surrogateMax {
+			return RuneError, 1, false
+		}
+		return r, 3, false
+	}
+
+	// need third continuation byte
+	if n < 4 {
+		return RuneError, 1, true
+	}
+	c3 := p[3]
+	if c3 < tx || t2 <= c3 {
+		return RuneError, 1, false
+	}
+
+	// 4-byte, 21-bit sequence?
+	if c0 < t5 {
+		r = rune(c0&mask4)<<18 | rune(c1&maskx)<<12 | rune(c2&maskx)<<6 | rune(c3&maskx)
+		if r <= rune3Max || MaxRune < r {
+			return RuneError, 1, false
+		}
+		return r, 4, false
+	}
+
+	// error
+	return RuneError, 1, false
+}
+
+func decodeRuneInStringInternal(s string) (r rune, size int, short bool) {
+	n := len(s)
+	if n < 1 {
+		return RuneError, 0, true
+	}
+	c0 := s[0]
+
+	// 1-byte, 7-bit sequence?
+	if c0 < tx {
+		return rune(c0), 1, false
+	}
+
+	// unexpected continuation byte?
+	if c0 < t2 {
+		return RuneError, 1, false
+	}
+
+	// need first continuation byte
+	if n < 2 {
+		return RuneError, 1, true
+	}
+	c1 := s[1]
+	if c1 < tx || t2 <= c1 {
+		return RuneError, 1, false
+	}
+
+	// 2-byte, 11-bit sequence?
+	if c0 < t3 {
+		r = rune(c0&mask2)<<6 | rune(c1&maskx)
+		if r <= rune1Max {
+			return RuneError, 1, false
+		}
+		return r, 2, false
+	}
+
+	// need second continuation byte
+	if n < 3 {
+		return RuneError, 1, true
+	}
+	c2 := s[2]
+	if c2 < tx || t2 <= c2 {
+		return RuneError, 1, false
+	}
+
+	// 3-byte, 16-bit sequence?
+	if c0 < t4 {
+		r = rune(c0&mask3)<<12 | rune(c1&maskx)<<6 | rune(c2&maskx)
+		if r <= rune2Max {
+			return RuneError, 1, false
+		}
+		if surrogateMin <= r && r <= surrogateMax {
+			return RuneError, 1, false
+		}
+		return r, 3, false
+	}
+
+	// need third continuation byte
+	if n < 4 {
+		return RuneError, 1, true
+	}
+	c3 := s[3]
+	if c3 < tx || t2 <= c3 {
+		return RuneError, 1, false
+	}
+
+	// 4-byte, 21-bit sequence?
+	if c0 < t5 {
+		r = rune(c0&mask4)<<18 | rune(c1&maskx)<<12 | rune(c2&maskx)<<6 | rune(c3&maskx)
+		if r <= rune3Max || MaxRune < r {
+			return RuneError, 1, false
+		}
+		return r, 4, false
+	}
+
+	// error
+	return RuneError, 1, false
+}
+
+// FullRune reports whether the bytes in p begin with a full UTF-8 encoding of a rune.
+// An invalid encoding is considered a full Rune since it will convert as a width-1 error rune.
+func FullRune(p []byte) bool {
+	_, _, short := decodeRuneInternal(p)
+	return !short
+}
+
+// FullRuneInString is like FullRune but its input is a string.
+func FullRuneInString(s string) bool {
+	_, _, short := decodeRuneInStringInternal(s)
+	return !short
+}
+
+// DecodeRune unpacks the first UTF-8 encoding in p and returns the rune and
+// its width in bytes. If p is empty it returns (RuneError, 0). Otherwise, if
+// the encoding is invalid, it returns (RuneError, 1). Both are impossible
+// results for correct UTF-8.
+//
+// An encoding is invalid if it is incorrect UTF-8, encodes a rune that is
+// out of range, or is not the shortest possible UTF-8 encoding for the
+// value. No other validation is performed.
+func DecodeRune(p []byte) (r rune, size int) {
+	r, size, _ = decodeRuneInternal(p)
+	return
+}
+
+// DecodeRuneInString is like DecodeRune but its input is a string. If s is
+// empty it returns (RuneError, 0). Otherwise, if the encoding is invalid, it
+// returns (RuneError, 1). Both are impossible results for correct UTF-8.
+//
+// An encoding is invalid if it is incorrect UTF-8, encodes a rune that is
+// out of range, or is not the shortest possible UTF-8 encoding for the
+// value. No other validation is performed.
+func DecodeRuneInString(s string) (r rune, size int) {
+	r, size, _ = decodeRuneInStringInternal(s)
+	return
+}
+
+// DecodeLastRune unpacks the last UTF-8 encoding in p and returns the rune and
+// its width in bytes. If p is empty it returns (RuneError, 0). Otherwise, if
+// the encoding is invalid, it returns (RuneError, 1). Both are impossible
+// results for correct UTF-8.
+//
+// An encoding is invalid if it is incorrect UTF-8, encodes a rune that is
+// out of range, or is not the shortest possible UTF-8 encoding for the
+// value. No other validation is performed.
+func DecodeLastRune(p []byte) (r rune, size int) {
+	end := len(p)
+	if end == 0 {
+		return RuneError, 0
+	}
+	start := end - 1
+	r = rune(p[start])
+	if r < RuneSelf {
+		return r, 1
+	}
+	// guard against O(n^2) behavior when traversing
+	// backwards through strings with long sequences of
+	// invalid UTF-8.
+	lim := end - UTFMax
+	if lim < 0 {
+		lim = 0
+	}
+	for start--; start >= lim; start-- {
+		if RuneStart(p[start]) {
+			break
+		}
+	}
+	if start < 0 {
+		start = 0
+	}
+	r, size = DecodeRune(p[start:end])
+	if start+size != end {
+		return RuneError, 1
+	}
+	return r, size
+}
+
+// DecodeLastRuneInString is like DecodeLastRune but its input is a string. If
+// s is empty it returns (RuneError, 0). Otherwise, if the encoding is invalid,
+// it returns (RuneError, 1). Both are impossible results for correct UTF-8.
+//
+// An encoding is invalid if it is incorrect UTF-8, encodes a rune that is
+// out of range, or is not the shortest possible UTF-8 encoding for the
+// value. No other validation is performed.
+func DecodeLastRuneInString(s string) (r rune, size int) {
+	end := len(s)
+	if end == 0 {
+		return RuneError, 0
+	}
+	start := end - 1
+	r = rune(s[start])
+	if r < RuneSelf {
+		return r, 1
+	}
+	// guard against O(n^2) behavior when traversing
+	// backwards through strings with long sequences of
+	// invalid UTF-8.
+	lim := end - UTFMax
+	if lim < 0 {
+		lim = 0
+	}
+	for start--; start >= lim; start-- {
+		if RuneStart(s[start]) {
+			break
+		}
+	}
+	if start < 0 {
+		start = 0
+	}
+	r, size = DecodeRuneInString(s[start:end])
+	if start+size != end {
+		return RuneError, 1
+	}
+	return r, size
+}
+
+// RuneLen returns the number of bytes required to encode the rune.
+// It returns -1 if the rune is not a valid value to encode in UTF-8.
+func RuneLen(r rune) int {
+	switch {
+	case r < 0:
+		return -1
+	case r <= rune1Max:
+		return 1
+	case r <= rune2Max:
+		return 2
+	case surrogateMin <= r && r <= surrogateMax:
+		return -1
+	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.
+// It returns the number of bytes written.
+func EncodeRune(p []byte, r rune) int {
+	// Negative values are erroneous.  Making it unsigned addresses the problem.
+	switch i := uint32(r); {
+	case i <= rune1Max:
+		p[0] = byte(r)
+		return 1
+	case i <= rune2Max:
+		p[0] = t2 | byte(r>>6)
+		p[1] = tx | byte(r)&maskx
+		return 2
+	case i > MaxRune, surrogateMin <= i && i <= surrogateMax:
+		r = RuneError
+		fallthrough
+	case i <= rune3Max:
+		p[0] = t3 | byte(r>>12)
+		p[1] = tx | byte(r>>6)&maskx
+		p[2] = tx | byte(r)&maskx
+		return 3
+	default:
+		p[0] = t4 | byte(r>>18)
+		p[1] = tx | byte(r>>12)&maskx
+		p[2] = tx | byte(r>>6)&maskx
+		p[3] = tx | byte(r)&maskx
+		return 4
+	}
+}
+
+// RuneCount returns the number of runes in p.  Erroneous and short
+// encodings are treated as single runes of width 1 byte.
+func RuneCount(p []byte) int {
+	i := 0
+	var n int
+	for n = 0; i < len(p); n++ {
+		if p[i] < RuneSelf {
+			i++
+		} else {
+			_, size := DecodeRune(p[i:])
+			i += size
+		}
+	}
+	return n
+}
+
+// RuneCountInString is like RuneCount but its input is a string.
+func RuneCountInString(s string) (n int) {
+	for range s {
+		n++
+	}
+	return
+}
+
+// RuneStart reports whether the byte could be the first byte of
+// an encoded rune.  Second and subsequent bytes always have the top
+// two bits set to 10.
+func RuneStart(b byte) bool { return b&0xC0 != 0x80 }
+
+// Valid reports whether p consists entirely of valid UTF-8-encoded runes.
+func Valid(p []byte) bool {
+	i := 0
+	for i < len(p) {
+		if p[i] < RuneSelf {
+			i++
+		} else {
+			_, size := DecodeRune(p[i:])
+			if size == 1 {
+				// All valid runes of size 1 (those
+				// below RuneSelf) were handled above.
+				// This must be a RuneError.
+				return false
+			}
+			i += size
+		}
+	}
+	return true
+}
+
+// ValidString reports whether s consists entirely of valid UTF-8-encoded runes.
+func ValidString(s string) bool {
+	for i, r := range s {
+		if r == RuneError {
+			// The RuneError value can be an error
+			// sentinel value (if it's size 1) or the same
+			// value encoded properly. Decode it to see if
+			// it's the 1 byte sentinel value.
+			_, size := DecodeRuneInString(s[i:])
+			if size == 1 {
+				return false
+			}
+		}
+	}
+	return true
+}
+
+// ValidRune reports whether r can be legally encoded as UTF-8.
+// Code points that are out of range or a surrogate half are illegal.
+func ValidRune(r rune) bool {
+	switch {
+	case r < 0:
+		return false
+	case surrogateMin <= r && r <= surrogateMax:
+		return false
+	case r > MaxRune:
+		return false
+	}
+	return true
+}