Stowage/go
2
0
Fork 0
mirror of https://github.com/golang/go.git synced 2025-12-08 06:10:04 +00:00
Code Issues Projects Releases Packages Wiki Activity

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

Browse source 
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
Download patch file Download diff file Expand all files Collapse all files

28
src/bytes/buffer.go
View file

@ -22,14 +22,18 @@ type Buffer struct {
} }
// The readOp constants describe the last action performed on // The readOp constants describe the last action performed on
// the buffer, so that UnreadRune and UnreadByte can // the buffer, so that UnreadRune and UnreadByte can check for
// check for invalid usage. // invalid usage. opReadRuneX constants are choosen such that
// converted to int they correspond to the rune size that was read.
type readOp int type readOp int
const ( const (
opInvalid readOp = iota // Non-read operation. opRead readOp = -1 // Any other read operation.
opReadRune // Read rune. opInvalid = 0 // Non-read operation.
opRead // Any other 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. // 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) b.Truncate(0)
return 0, 0, io.EOF return 0, 0, io.EOF
} }
b.lastRead = opReadRune
c := b.buf[b.off] c := b.buf[b.off]
if c < utf8.RuneSelf { if c < utf8.RuneSelf {
b.off++ b.off++
b.lastRead = opReadRune1
return rune(c), 1, nil return rune(c), 1, nil
} }
r, n := utf8.DecodeRune(b.buf[b.off:]) r, n := utf8.DecodeRune(b.buf[b.off:])
b.off += n b.off += n
b.lastRead = readOp(n)
return r, n, nil 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 // it is stricter than UnreadByte, which will unread the last byte
// from any read operation.) // from any read operation.)
func (b *Buffer) UnreadRune() error { func (b *Buffer) UnreadRune() error {
if b.lastRead != opReadRune { if b.lastRead <= opInvalid {
return errors.New("bytes.Buffer: UnreadRune: previous operation was not ReadRune") return errors.New("bytes.Buffer: UnreadRune: previous operation was not ReadRune")
} }
b.lastRead = opInvalid if b.off >= int(b.lastRead) {
if b.off > 0 { b.off -= int(b.lastRead)
_, n := utf8.DecodeLastRune(b.buf[0:b.off])
b.off -= n
} }
b.lastRead = opInvalid
return nil return nil
} }
@ -351,7 +355,7 @@ func (b *Buffer) UnreadRune() error {
// read operation. If write has happened since the last read, UnreadByte // read operation. If write has happened since the last read, UnreadByte
// returns an error. // returns an error.
func (b *Buffer) UnreadByte() 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") return errors.New("bytes.Buffer: UnreadByte: previous operation was not a read")
} }
b.lastRead = opInvalid b.lastRead = opInvalid