From 9e7f3a46d3682c3206202e3421d5034193feb2f7 Mon Sep 17 00:00:00 2001
From: Rob Pike <r@golang.org>
Date: Tue, 22 Sep 2009 14:53:48 -0700
Subject: [PATCH] restore the old algorithm. the new one is more memory
 efficient in large cases but too slow across the board.

R=rsc
DELTA=315  (50 added, 219 deleted, 46 changed)
OCL=34868
CL=34902
---
 src/pkg/bytes/buffer.go | 355 +++++++++++-----------------------------
 1 file changed, 93 insertions(+), 262 deletions(-)

diff --git a/src/pkg/bytes/buffer.go b/src/pkg/bytes/buffer.go
index cdc4a09939..0080d248b3 100644
--- a/src/pkg/bytes/buffer.go
+++ b/src/pkg/bytes/buffer.go
@@ -4,131 +4,11 @@
 
 package bytes
 
-import "os"
+// Simple byte buffer for marshaling data.
 
-// Efficient construction of large strings and byte arrays.
-// Implements io.Reader and io.Writer.
-
-// A Buffer provides efficient construction of large strings
-// and slices of bytes.  It implements io.Reader and io.Writer.
-// Appends (writes) are efficient.
-// The zero value for Buffer is an empty buffer ready to use.
-type Buffer struct {
-	blk	[]block;
-	len	int;
-	oneByte	[1]byte;
-}
-
-// There are two kinds of block: a string or a []byte.
-// When the user writes big strings, we add string blocks;
-// when the user writes big byte slices, we add []byte blocks.
-// Small writes are coalesced onto the end of the last block,
-// whatever it is.
-// This strategy is intended to reduce unnecessary allocation.
-type block interface {
-	Len()	int;
-	String()	string;
-	appendBytes(s []byte);
-	appendString(s string);
-	setSlice(m, n int);
-}
-
-// stringBlocks represent strings. We use pointer receivers
-// so append and setSlice can overwrite the receiver.
-type stringBlock string
-
-func (b *stringBlock) Len() int {
-	return len(*b)
-}
-
-func (b *stringBlock) String() string {
-	return string(*b)
-}
-
-func (b *stringBlock) appendBytes(s []byte) {
-	*b += stringBlock(s)
-}
-
-func (b *stringBlock) appendString(s string) {
-	*b = stringBlock(s)
-}
-
-func (b *stringBlock) setSlice(m, n int) {
-	*b = (*b)[m:n]
-}
-
-// byteBlock represent slices of bytes.  We use pointer receivers
-// so append and setSlice can overwrite the receiver.
-type byteBlock []byte
-
-func (b *byteBlock) Len() int {
-	return len(*b)
-}
-
-func (b *byteBlock) String() string {
-	return string(*b)
-}
-
-func (b *byteBlock) resize(max int) {
-	by := []byte(*b);
-	if cap(by) >= max {
-		by = by[0:max];
-	} else {
-		nby := make([]byte, max, 3*(max+10)/2);
-		copyBytes(nby, 0, by);
-		by = nby;
-	}
-	*b = by;
-}
-
-func (b *byteBlock) appendBytes(s []byte) {
-	curLen := b.Len();
-	b.resize(curLen + len(s));
-	copyBytes([]byte(*b), curLen, s);
-}
-
-func (b *byteBlock) appendString(s string) {
-	curLen := b.Len();
-	b.resize(curLen + len(s));
-	copyString([]byte(*b), curLen, s);
-}
-
-func (b *byteBlock) setSlice(m, n int) {
-	*b = (*b)[m:n]
-}
-
-// Because the user may overwrite the contents of byte slices, we need
-// to make a copy.  Allocation strategy: leave some space on the end so
-// small subsequent writes can avoid another allocation.  The input
-// is known to be non-empty.
-func newByteBlock(s []byte) *byteBlock {
-	l := len(s);
-	// Capacity with room to grow.  If small, allocate a mininum.  If medium,
-	// double the size.  If huge, use the size plus epsilon (room for a newline,
-	// at least).
-	c := l;
-	switch {
-	case l < 32:
-		c = 64
-	case l < 1<<18:
-		c *= 2;
-	default:
-		c += 8
-	}
-	b := make([]byte, l, c);
-	copyBytes(b, 0, s);
-	return &b;
-}
-
-// Copy from block to byte array at offset doff.  Assume there's room.
-func copy(dst []byte, doff int, src block) {
-	switch s := src.(type) {
-	case *stringBlock:
-		copyString(dst, doff, string(*s));
-	case *byteBlock:
-		copyBytes(dst, doff, []byte(*s));
-	}
-}
+import (
+	"os";
+)
 
 // Copy from string to byte array at offset doff.  Assume there's room.
 func copyString(dst []byte, doff int, str string) {
@@ -146,134 +26,105 @@ func copyBytes(dst []byte, doff int, src []byte) {
 	}
 }
 
-// Bytes returns the contents of the unread portion of the buffer
-// as a byte array.
+// 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)]
+	oneByte	[]byte;	// avoid allocation of slice on each WriteByte
+}
+
+// Bytes returns the contents of the unread portion of the buffer;
+// len(b.Bytes()) == b.Len().
 func (b *Buffer) Bytes() []byte {
-	n := b.len;
-	bytes := make([]byte, n);
-	nbytes := 0;
-	for _, s := range b.blk {
-		copy(bytes, nbytes, s);
-		nbytes += s.Len();
-	}
-	return bytes;
+	return b.buf[b.off : len(b.buf)]
 }
 
 // String returns the contents of the unread portion of the buffer
 // as a string.
 func (b *Buffer) String() string {
-	if len(b.blk) == 1 {	// important special case
-		return b.blk[0].String()
-	}
-	return string(b.Bytes())
+	return string(b.buf[b.off : len(b.buf)])
 }
 
-// Len returns the number of bytes in the unread portion of the buffer;
-// b.Len() == len(b.Bytes()) == len(b.String()).
+// Len returns the number of bytes of the unread portion of the buffer;
+// b.Len() == len(b.Bytes()).
 func (b *Buffer) Len() int {
-	return b.len
+	return len(b.buf) - b.off
 }
 
 // Truncate discards all but the first n unread bytes from the buffer.
+// It is an error to call b.Truncate(n) with n > b.Len().
 func (b *Buffer) Truncate(n int) {
-	b.len = 0;	// recompute during scan.
-	for i, s := range b.blk {
-		if n <= 0 {
-			b.blk = b.blk[0:i];
-			break;
-		}
-		if l := s.Len(); n < l {
-			b.blk[i].setSlice(0, n);
-			b.len += n;
-			n = 0;
-		} else {
-			b.len += l;
-			n -= l;
-		}
+	if n == 0 {
+		// Reuse buffer space.
+		b.off = 0;
 	}
+	b.buf = b.buf[0 : b.off + n];
 }
 
 // Reset resets the buffer so it has no content.
 // b.Reset() is the same as b.Truncate(0).
 func (b *Buffer) Reset() {
-	b.blk = b.blk[0:0];
-	b.len = 0;
+	b.Truncate(0);
 }
 
-// Can n bytes be appended efficiently to the end of the final string?
-func (b *Buffer) canCombine(n int) bool {
-	return len(b.blk) > 0 && n+b.blk[len(b.blk)-1].Len() <= 64
+// 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();
+	n = len(p);
+
+	if len(b.buf) + n > cap(b.buf) {
+		// not enough space at end
+		buf := b.buf;
+		if m + n > cap(b.buf) {
+			// not enough space anywhere
+			buf = make([]byte, 2*cap(b.buf) + n)
+		}
+		copyBytes(buf, 0, b.buf[b.off:b.off+m]);
+		b.buf = buf;
+		b.off = 0
+	}
+
+	b.buf = b.buf[0 : b.off + m + n];
+	copyBytes(b.buf, b.off + m, p);
+	return n, nil
 }
 
-// WriteString appends string s to the buffer.  The return
+// 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();
 	n = len(s);
-	if n == 0 {
-		return
-	}
-	b.len += n;
-	numStr := len(b.blk);
-	// Special case: If the last piece is short and this one is short,
-	// combine them and avoid growing the list.
-	if b.canCombine(n) {
-		b.blk[numStr-1].appendString(s);
-		return
-	}
-	if cap(b.blk) == numStr {
-		nstr := make([]block, numStr, 3*(numStr+10)/2);
-		for i, s := range b.blk {
-			nstr[i] = s;
-		}
-		b.blk = nstr;
-	}
-	b.blk = b.blk[0:numStr+1];
-	// The string is immutable; no need to make a copy.
-	b.blk[numStr] = (*stringBlock)(&s);
-	return
-}
 
-// 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) {
-	n = len(p);
-	if n == 0 {
-		return
-	}
-	b.len += n;
-	numStr := len(b.blk);
-	// Special case: If the last piece is short and this one is short,
-	// combine them and avoid growing the list.
-	if b.canCombine(n) {
-		b.blk[numStr-1].appendBytes(p);
-		return
-	}
-	if cap(b.blk) == numStr {
-		nstr := make([]block, numStr, 3*(numStr+10)/2);
-		for i, s := range b.blk {
-			nstr[i] = s;
+	if len(b.buf) + n > cap(b.buf) {
+		// not enough space at end
+		buf := b.buf;
+		if m + n > cap(b.buf) {
+			// not enough space anywhere
+			buf = make([]byte, 2*cap(b.buf) + n)
 		}
-		b.blk = nstr;
+		copyBytes(buf, 0, b.buf[b.off:b.off+m]);
+		b.buf = buf;
+		b.off = 0
 	}
-	b.blk = b.blk[0:numStr+1];
-	// Need to copy the data - user might overwrite the data.
-	b.blk[numStr] = newByteBlock(p);
-	return
+
+	b.buf = b.buf[0 : b.off + m + n];
+	copyString(b.buf, b.off+m, s);
+	return n, nil
 }
 
 // WriteByte appends the byte c to the buffer.
 // The returned error is always nil, but is included
 // to match bufio.Writer's WriteByte.
 func (b *Buffer) WriteByte(c byte) os.Error {
-	b.oneByte[0] = c;
-	// For WriteByte, canCombine is almost always true so it's worth
-	// doing here.
-	if b.canCombine(1) {
-		b.blk[len(b.blk)-1].appendBytes(&b.oneByte);
-		b.len++;
-		return nil
+	if b.oneByte == nil {
+		// Only happens once per Buffer, and then we have a slice.
+		b.oneByte = make([]byte, 1);
 	}
-	b.Write(&b.oneByte);
+	b.oneByte[0] = c;
+	b.Write(b.oneByte);
 	return nil;
 }
 
@@ -282,63 +133,43 @@ func (b *Buffer) WriteByte(c byte) os.Error {
 // buffer has no data to return, err is os.EOF even if len(p) is zero;
 // otherwise it is nil.
 func (b *Buffer) Read(p []byte) (n int, err os.Error) {
-	if len(b.blk) == 0 {
+	if b.off >= len(b.buf) {
 		return 0, os.EOF
 	}
-	for len(b.blk) > 0 {
-		blk := b.blk[0];
-		m := len(p) - n;
-		if l := blk.Len(); m >= l {
-			// consume all of this string.
-			copy(p, n, blk);
-			n += l;
-			b.blk = b.blk[1:len(b.blk)];
-		} else {
-			// consume some of this block; it's the last piece.
-			switch b := blk.(type) {
-			case *stringBlock:
-				copyString(p, n, string(*b)[0:m]);
-			case *byteBlock:
-				copyBytes(p, n, []byte(*b)[0:m]);
-			}
-			n += m;
-			b.blk[0].setSlice(m, l);
-			break;
-		}
+	m := b.Len();
+	n = len(p);
+
+	if n > m {
+		// more bytes requested than available
+		n = m
 	}
-	b.len -= n;
-	return
+
+	copyBytes(p, 0, b.buf[b.off:b.off+n]);
+	b.off += n;
+	return n, err
 }
 
 // ReadByte reads and returns the next byte from the buffer.
 // If no byte is available, it returns error os.EOF.
 func (b *Buffer) ReadByte() (c byte, err os.Error) {
-	if _, err := b.Read(&b.oneByte); err != nil {
-		return 0, err
+	if b.off >= len(b.buf) {
+		return 0, os.EOF;
 	}
-	return b.oneByte[0], nil
+	c = b.buf[b.off];
+	b.off++;
+	return c, nil;
 }
 
-// NewBufferString creates and initializes a new Buffer
-// using a string as its initial contents.
-func NewBufferString(str string) *Buffer {
-	b := new(Buffer);
-	if len(str) > 0 {
-		b.blk = make([]block, 1, 10);	// room to grow
-		b.blk[0] = (*stringBlock)(&str);
-	}
-	b.len = len(str);
-	return b;
+// NewBuffer creates and initializes a new Buffer
+// using buf as its initial contents.
+func NewBuffer(buf []byte) *Buffer {
+	return &Buffer{buf: buf};
 }
 
-// NewBuffer creates and initializes a new Buffer
-// using a byte slice as its initial contents.
-func NewBuffer(by []byte) *Buffer {
-	b := new(Buffer);
-	if len(by) > 0 {
-		b.blk = make([]block, 1, 10);	// room to grow
-		b.blk[0] = (*byteBlock)(&by);
-	}
-	b.len = len(by);
-	return b;
+// NewBufferString creates and initializes a new Buffer
+// using string s as its initial contents.
+func NewBufferString(s string) *Buffer {
+	buf := make([]byte, len(s));
+	copyString(buf, 0, s);
+	return &Buffer{buf: buf};
 }
-- 
2.48.1