better io.ByteBuffer implementation:

- more light-weight
- better buffer management
- added test cases

R=r
DELTA=227  (167 added, 35 deleted, 25 changed)
OCL=28252
CL=28289

1 files changed, 45 insertions, 59 deletions

diff --git a/src/lib/io/bytebuffer.go b/src/lib/io/bytebuffer.go
index 9c78e8566..011166e9c 100644
--- a/src/lib/io/bytebuffer.go
+++ b/src/lib/io/bytebuffer.go
@@ -11,11 +11,8 @@ import (
 	"os";
 )
 
-
-// TODO(r): Do better memory management.
-
 func bytecopy(dst []byte, doff int, src []byte, soff int, count int) {
-	for i := 0; i < count; i++ {
+	for ; count > 0; count-- {
 		dst[doff] = src[soff];
 		doff++;
 		soff++;
@@ -26,79 +23,68 @@ func bytecopy(dst []byte, doff int, src []byte, soff int, count int) {
 // connected to a buffer of bytes.
 // The zero value for ByteBuffer is an empty buffer ready to use.
 type ByteBuffer struct {
-	buf	[]byte;
-	off	int;	// Read from here
-	len	int;	// Write to here
-	cap	int;
+	buf	[]byte;	// contents are the bytes buf[off : len(buf)]
+	off	int;	// read at &buf[off], write at &buf[len(buf)]
+}
+
+// Data returns the contents of the unread portion of the buffer;
+// len(b.Data()) == b.Len().
+func (b *ByteBuffer) Data() []byte {
+	return b.buf[b.off : len(b.buf)]
+}
+
+// Len returns the number of bytes of the unread portion of the buffer;
+// b.Len() == len(b.Data()).
+func (b *ByteBuffer) Len() int {
+	return len(b.buf) - b.off
 }
 
 // Reset resets the buffer so it has no content.
 func (b *ByteBuffer) Reset() {
-	b.off = 0;
-	b.len = 0;
+	b.off = len(b.buf)
 }
 
 // Write appends the contents of p to the buffer.  The return
-// value is the length of p; err is always nil.
+// value n is the length of p; err is always nil.
 func (b *ByteBuffer) Write(p []byte) (n int, err os.Error) {
-	plen := len(p);
-	if len(b.buf) == 0 {
-		b.cap = plen + 1024;
-		b.buf = make([]byte, b.cap);
-		b.len = 0;
-	}
-	if b.len + plen > b.cap {
-		b.cap = 2*(b.cap + plen);
-		nb := make([]byte, b.cap);
-		bytecopy(nb, 0, b.buf, 0, b.len);
-		b.buf = nb;
+	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)
+		}
+		bytecopy(buf, 0, b.buf, b.off, m);
+		b.buf = buf;
+		b.off = 0
 	}
-	bytecopy(b.buf, b.len, p, 0, plen);
-	b.len += plen;
-	return plen, nil;
+
+	b.buf = b.buf[0 : b.off + m + n];
+	bytecopy(b.buf, b.off + m, p, 0, n);
+	return n, nil
 }
 
 // Read reads the next len(p) bytes from the buffer or until the buffer
-// is drained.  The return value is the number of bytes read; err is always nil.
+// is drained.  The return value n is the number of bytes read; err is always nil.
 func (b *ByteBuffer) Read(p []byte) (n int, err os.Error) {
-	plen := len(p);
-	if len(b.buf) == 0 {
-		return 0, nil
-	}
-	if b.off == b.len {	// empty buffer
-		b.Reset();
-		return 0, nil
-	}
-	if plen > b.len - b.off {
-		plen = b.len - b.off
-	}
-	bytecopy(p, 0, b.buf, b.off, plen);
-	b.off += plen;
-	return plen, nil;
-}
-
-// Len returns the length of the underlying buffer.
-func (b *ByteBuffer) Len() int {
-	return b.len
-}
+	m := b.Len();
+	n = len(p);
 
-// Off returns the location within the buffer of the next byte to be read.
-func (b *ByteBuffer) Off() int {
-	return b.off
-}
+	if n > m {
+		// more bytes requested than available
+		n = m
+	}
 
-// Data returns the contents of the unread portion of the buffer.
-func (b *ByteBuffer) Data() []byte {
-	return b.buf[b.off:b.len]
+	bytecopy(p, 0, b.buf, b.off, n);
+	b.off += n;
+	return n, nil
 }
 
 // NewByteBufferFromArray creates and initializes a new ByteBuffer
 // with buf as its initial contents.
 func NewByteBufferFromArray(buf []byte) *ByteBuffer {
-	b := new(ByteBuffer);
-	b.buf = buf;
-	b.off = 0;
-	b.len = len(buf);
-	b.cap = len(buf);
-	return b;
+	return &ByteBuffer{buf, 0};
 }