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bytes: encode size of rune read by ReadRune into lastRead to speed up UnreadRune

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In ReadRune store the size of the rune that was read into lastRead
to avoid the need to call DecodeRuneLast in UnreadRune.

fmt:
name        old time/op  new time/op  delta
ScanInts-4   481µs ± 4%   458µs ± 3%  -4.64%  (p=0.000 n=20+20)

Change-Id: I500848e663a975f426402a4b3d27a541e5cac06c
Reviewed-on: https://go-review.googlesource.com/28817
Reviewed-by: Russ Cox <rsc@golang.org>
Run-TryBot: Russ Cox <rsc@golang.org>
Run-TryBot: Martin Möhrmann <martisch@uos.de>
TryBot-Result: Gobot Gobot <gobot@golang.org>
This commit is contained in:
Martin Möhrmann 2016-09-06 13:42:49 +02:00 • committed by Brad Fitzpatrick
parent 1e775fe4a3
commit 99df54f196
1 changed files with 16 additions and 12 deletions
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28
src/bytes/buffer.go
View file

@ -22,14 +22,18 @@ type Buffer struct {
}
// 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 choosen 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.
@ -319,14 +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
}
@ -336,14 +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
}
@ -351,7 +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