bytes: shuffle implementation, making WriteByte 50% faster
R=r
CC=golang-dev
https://golang.org/cl/920041
diff --git a/src/pkg/bytes/buffer.go b/src/pkg/bytes/buffer.go
index acd4523..faccca3 100644
--- a/src/pkg/bytes/buffer.go
+++ b/src/pkg/bytes/buffer.go
@@ -63,54 +63,44 @@
// b.Reset() is the same as b.Truncate(0).
func (b *Buffer) Reset() { b.Truncate(0) }
-// Resize buffer to guarantee enough space for n more bytes.
-// After this call, the state of b.buf is inconsistent.
-// It must be fixed up as is done in Write and WriteString.
-func (b *Buffer) resize(n int) {
- var buf []byte
- if b.buf == nil && n <= len(b.bootstrap) {
- buf = &b.bootstrap
- } else {
- // not enough space anywhere
- buf = make([]byte, 2*cap(b.buf)+n)
- copy(buf, b.buf[b.off:])
+// Grow buffer to guarantee space for n more bytes.
+// Return index where bytes should be written.
+func (b *Buffer) grow(n int) int {
+ m := b.Len()
+ // If buffer is empty, reset to recover space.
+ if m == 0 && b.off != 0 {
+ b.Truncate(0)
}
- b.buf = buf
- b.off = 0
+ if len(b.buf)+n > cap(b.buf) {
+ var buf []byte
+ if b.buf == nil && n <= len(b.bootstrap) {
+ buf = &b.bootstrap
+ } else {
+ // not enough space anywhere
+ buf = make([]byte, 2*cap(b.buf)+n)
+ copy(buf, b.buf[b.off:])
+ }
+ b.buf = buf
+ b.off = 0
+ }
+ b.buf = b.buf[0 : b.off+m+n]
+ return b.off + m
}
// Write appends the contents of p to the buffer. The return
// value n is the length of p; err is always nil.
func (b *Buffer) Write(p []byte) (n int, err os.Error) {
- m := b.Len()
- // If buffer is empty, reset to recover space.
- if m == 0 && b.off != 0 {
- b.Truncate(0)
- }
- n = len(p)
- if len(b.buf)+n > cap(b.buf) {
- b.resize(n)
- }
- b.buf = b.buf[0 : b.off+m+n]
- copy(b.buf[b.off+m:], p)
- return n, nil
+ m := b.grow(len(p))
+ copy(b.buf[m:], p)
+ return len(p), nil
}
// WriteString appends the contents of s to the buffer. The return
// value n is the length of s; err is always nil.
func (b *Buffer) WriteString(s string) (n int, err os.Error) {
- m := b.Len()
- // If buffer is empty, reset to recover space.
- if m == 0 && b.off != 0 {
- b.Truncate(0)
- }
- n = len(s)
- if len(b.buf)+n > cap(b.buf) {
- b.resize(n)
- }
- b.buf = b.buf[0 : b.off+m+n]
- copyString(b.buf, b.off+m, s)
- return n, nil
+ m := b.grow(len(s))
+ copyString(b.buf, m, s)
+ return len(s), nil
}
// MinRead is the minimum slice size passed to a Read call by
@@ -177,8 +167,8 @@
// The returned error is always nil, but is included
// to match bufio.Writer's WriteByte.
func (b *Buffer) WriteByte(c byte) os.Error {
- b.runeBytes[0] = c
- b.Write(b.runeBytes[0:1])
+ m := b.grow(1)
+ b.buf[m] = c
return nil
}
