1 files changed, 24 insertions, 19 deletions

diff --git a/libgo/go/bytes/buffer.go b/libgo/go/bytes/buffer.go
index 9154a1b9545..196419dc3da 100644
--- a/libgo/go/bytes/buffer.go
+++ b/libgo/go/bytes/buffer.go
@@ -15,22 +15,25 @@ import (
 // A Buffer is a variable-sized buffer of bytes with Read and Write methods.
 // The zero value for Buffer is an empty buffer ready to use.
 type Buffer struct {
-	buf       []byte            // contents are the bytes buf[off : len(buf)]
-	off       int               // read at &buf[off], write at &buf[len(buf)]
-	runeBytes [utf8.UTFMax]byte // avoid allocation of slice on each call to WriteRune
-	bootstrap [64]byte          // memory to hold first slice; helps small buffers avoid allocation.
-	lastRead  readOp            // last read operation, so that Unread* can work correctly.
+	buf       []byte   // contents are the bytes buf[off : len(buf)]
+	off       int      // read at &buf[off], write at &buf[len(buf)]
+	bootstrap [64]byte // memory to hold first slice; helps small buffers avoid allocation.
+	lastRead  readOp   // last read operation, so that Unread* can work correctly.
 }
 
 // The readOp constants describe the last action performed on
-// the buffer, so that UnreadRune and UnreadByte can
-// check for invalid usage.
+// the buffer, so that UnreadRune and UnreadByte can check for
+// invalid usage. opReadRuneX constants are chosen such that
+// converted to int they correspond to the rune size that was read.
 type readOp int
 
 const (
-	opInvalid  readOp = iota // Non-read operation.
-	opReadRune               // Read rune.
-	opRead                   // Any other read operation.
+	opRead      readOp = -1 // Any other read operation.
+	opInvalid          = 0  // Non-read operation.
+	opReadRune1        = 1  // Read rune of size 1.
+	opReadRune2        = 2  // Read rune of size 2.
+	opReadRune3        = 3  // Read rune of size 3.
+	opReadRune4        = 4  // Read rune of size 4.
 )
 
 // ErrTooLarge is passed to panic if memory cannot be allocated to store data in a buffer.
@@ -246,8 +249,10 @@ func (b *Buffer) WriteRune(r rune) (n int, err error) {
 		b.WriteByte(byte(r))
 		return 1, nil
 	}
-	n = utf8.EncodeRune(b.runeBytes[0:], r)
-	b.Write(b.runeBytes[0:n])
+	b.lastRead = opInvalid
+	m := b.grow(utf8.UTFMax)
+	n = utf8.EncodeRune(b.buf[m:m+utf8.UTFMax], r)
+	b.buf = b.buf[:m+n]
 	return n, nil
 }
 
@@ -318,14 +323,15 @@ func (b *Buffer) ReadRune() (r rune, size int, err error) {
 		b.Truncate(0)
 		return 0, 0, io.EOF
 	}
-	b.lastRead = opReadRune
 	c := b.buf[b.off]
 	if c < utf8.RuneSelf {
 		b.off++
+		b.lastRead = opReadRune1
 		return rune(c), 1, nil
 	}
 	r, n := utf8.DecodeRune(b.buf[b.off:])
 	b.off += n
+	b.lastRead = readOp(n)
 	return r, n, nil
 }
 
@@ -335,14 +341,13 @@ func (b *Buffer) ReadRune() (r rune, size int, err error) {
 // it is stricter than UnreadByte, which will unread the last byte
 // from any read operation.)
 func (b *Buffer) UnreadRune() error {
-	if b.lastRead != opReadRune {
+	if b.lastRead <= opInvalid {
 		return errors.New("bytes.Buffer: UnreadRune: previous operation was not ReadRune")
 	}
-	b.lastRead = opInvalid
-	if b.off > 0 {
-		_, n := utf8.DecodeLastRune(b.buf[0:b.off])
-		b.off -= n
+	if b.off >= int(b.lastRead) {
+		b.off -= int(b.lastRead)
 	}
+	b.lastRead = opInvalid
 	return nil
 }
 
@@ -350,7 +355,7 @@ func (b *Buffer) UnreadRune() error {
 // read operation. If write has happened since the last read, UnreadByte
 // returns an error.
 func (b *Buffer) UnreadByte() error {
-	if b.lastRead != opReadRune && b.lastRead != opRead {
+	if b.lastRead == opInvalid {
 		return errors.New("bytes.Buffer: UnreadByte: previous operation was not a read")
 	}
 	b.lastRead = opInvalid