[dev.power64] code review 152570049: all: merge default into dev.power64

src/unicode/utf8/utf8.go

 // 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.
@@ skipping 193 matching lines @@
         _, _, 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 the encoding is invalid, it returns (RuneError, 1), an impossible result for correct UTF-8.
+// 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 the encoding is invalid, it returns (RuneError, 1), an impossible result for correct UTF-8.
+// 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 the encoding is invalid, it returns (RuneError, 1), an impossible result for correct UTF-8.
+// 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])
@@ skipping 15 matching lines @@
         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 the encoding is invalid, it returns (RuneError, 1), an impossible result for correct UTF-8.
+// 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])
@@ skipping 143 matching lines @@
         switch {
         case r < 0:
                 return false
         case surrogateMin <= r && r <= surrogateMax:
                 return false
         case r > MaxRune:
                 return false
         }
         return true
 }