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better io.ByteBuffer implementation:

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

R=r
DELTA=227  (167 added, 35 deleted, 25 changed)
OCL=28252
CL=28289
This commit is contained in:
Robert Griesemer 2009-05-05 12:00:52 -07:00
parent 747e26166a
commit eea33fc69c
2 changed files with 191 additions and 59 deletions
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104
src/lib/io/bytebuffer.go
View file

@ -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;
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
}
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;
}
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;
}
m := b.Len();
n = len(p);
// Len returns the length of the underlying buffer.
func (b *ByteBuffer) Len() int {
return b.len
}
if n > m {
// more bytes requested than available
n = m
}
// Off returns the location within the buffer of the next byte to be read.
func (b *ByteBuffer) Off() int {
return b.off
}
// 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};
}