mirror of
https://github.com/golang/go
synced 2024-11-25 15:08:02 -07:00
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
This commit is contained in:
Rob Pike
parent
b9493ded12
commit
9e7f3a46d3
@ -4,131 +4,11 @@
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package bytes
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import "os"
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// Simple byte buffer for marshaling data.
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// Efficient construction of large strings and byte arrays.
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// Implements io.Reader and io.Writer.
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// A Buffer provides efficient construction of large strings
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// and slices of bytes. It implements io.Reader and io.Writer.
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// Appends (writes) are efficient.
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// The zero value for Buffer is an empty buffer ready to use.
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type Buffer struct {
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blk []block;
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len int;
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oneByte [1]byte;
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}
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// There are two kinds of block: a string or a []byte.
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// When the user writes big strings, we add string blocks;
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// when the user writes big byte slices, we add []byte blocks.
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// Small writes are coalesced onto the end of the last block,
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// whatever it is.
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// This strategy is intended to reduce unnecessary allocation.
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type block interface {
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Len() int;
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String() string;
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appendBytes(s []byte);
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appendString(s string);
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setSlice(m, n int);
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}
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// stringBlocks represent strings. We use pointer receivers
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// so append and setSlice can overwrite the receiver.
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type stringBlock string
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func (b *stringBlock) Len() int {
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return len(*b)
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}
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func (b *stringBlock) String() string {
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return string(*b)
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}
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func (b *stringBlock) appendBytes(s []byte) {
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*b += stringBlock(s)
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}
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func (b *stringBlock) appendString(s string) {
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*b = stringBlock(s)
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}
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func (b *stringBlock) setSlice(m, n int) {
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*b = (*b)[m:n]
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}
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// byteBlock represent slices of bytes. We use pointer receivers
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// so append and setSlice can overwrite the receiver.
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type byteBlock []byte
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func (b *byteBlock) Len() int {
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return len(*b)
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}
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func (b *byteBlock) String() string {
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return string(*b)
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}
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func (b *byteBlock) resize(max int) {
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by := []byte(*b);
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if cap(by) >= max {
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by = by[0:max];
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} else {
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nby := make([]byte, max, 3*(max+10)/2);
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copyBytes(nby, 0, by);
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by = nby;
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}
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*b = by;
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}
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func (b *byteBlock) appendBytes(s []byte) {
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curLen := b.Len();
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b.resize(curLen + len(s));
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copyBytes([]byte(*b), curLen, s);
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}
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func (b *byteBlock) appendString(s string) {
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curLen := b.Len();
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b.resize(curLen + len(s));
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copyString([]byte(*b), curLen, s);
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}
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func (b *byteBlock) setSlice(m, n int) {
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*b = (*b)[m:n]
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}
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// Because the user may overwrite the contents of byte slices, we need
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// to make a copy. Allocation strategy: leave some space on the end so
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// small subsequent writes can avoid another allocation. The input
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// is known to be non-empty.
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func newByteBlock(s []byte) *byteBlock {
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l := len(s);
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// Capacity with room to grow. If small, allocate a mininum. If medium,
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// double the size. If huge, use the size plus epsilon (room for a newline,
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// at least).
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c := l;
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switch {
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case l < 32:
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c = 64
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case l < 1<<18:
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c *= 2;
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default:
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c += 8
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}
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b := make([]byte, l, c);
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copyBytes(b, 0, s);
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return &b;
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}
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// Copy from block to byte array at offset doff. Assume there's room.
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func copy(dst []byte, doff int, src block) {
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switch s := src.(type) {
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case *stringBlock:
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copyString(dst, doff, string(*s));
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case *byteBlock:
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copyBytes(dst, doff, []byte(*s));
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}
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}
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import (
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"os";
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)
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// Copy from string to byte array at offset doff. Assume there's room.
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func copyString(dst []byte, doff int, str string) {
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@ -146,134 +26,105 @@ func copyBytes(dst []byte, doff int, src []byte) {
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}
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}
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// Bytes returns the contents of the unread portion of the buffer
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// as a byte array.
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// A Buffer is a variable-sized buffer of bytes
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// with Read and Write methods.
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// The zero value for Buffer is an empty buffer ready to use.
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type Buffer struct {
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buf []byte; // contents are the bytes buf[off : len(buf)]
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off int; // read at &buf[off], write at &buf[len(buf)]
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oneByte []byte; // avoid allocation of slice on each WriteByte
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}
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// Bytes returns the contents of the unread portion of the buffer;
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// len(b.Bytes()) == b.Len().
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func (b *Buffer) Bytes() []byte {
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n := b.len;
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bytes := make([]byte, n);
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nbytes := 0;
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for _, s := range b.blk {
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copy(bytes, nbytes, s);
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nbytes += s.Len();
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}
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return bytes;
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return b.buf[b.off : len(b.buf)]
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}
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// String returns the contents of the unread portion of the buffer
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// as a string.
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func (b *Buffer) String() string {
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if len(b.blk) == 1 { // important special case
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return b.blk[0].String()
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}
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return string(b.Bytes())
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return string(b.buf[b.off : len(b.buf)])
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}
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// Len returns the number of bytes in the unread portion of the buffer;
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// b.Len() == len(b.Bytes()) == len(b.String()).
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// Len returns the number of bytes of the unread portion of the buffer;
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// b.Len() == len(b.Bytes()).
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func (b *Buffer) Len() int {
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return b.len
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return len(b.buf) - b.off
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}
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// Truncate discards all but the first n unread bytes from the buffer.
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// It is an error to call b.Truncate(n) with n > b.Len().
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func (b *Buffer) Truncate(n int) {
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b.len = 0; // recompute during scan.
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for i, s := range b.blk {
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if n <= 0 {
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b.blk = b.blk[0:i];
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break;
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}
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if l := s.Len(); n < l {
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b.blk[i].setSlice(0, n);
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b.len += n;
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n = 0;
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} else {
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b.len += l;
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n -= l;
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}
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if n == 0 {
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// Reuse buffer space.
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b.off = 0;
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}
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b.buf = b.buf[0 : b.off + n];
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}
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// Reset resets the buffer so it has no content.
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// b.Reset() is the same as b.Truncate(0).
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func (b *Buffer) Reset() {
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b.blk = b.blk[0:0];
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b.len = 0;
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}
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// Can n bytes be appended efficiently to the end of the final string?
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func (b *Buffer) canCombine(n int) bool {
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return len(b.blk) > 0 && n+b.blk[len(b.blk)-1].Len() <= 64
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}
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// WriteString appends string s to the buffer. The return
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// value n is the length of s; err is always nil.
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func (b *Buffer) WriteString(s string) (n int, err os.Error) {
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n = len(s);
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if n == 0 {
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return
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}
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b.len += n;
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numStr := len(b.blk);
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// Special case: If the last piece is short and this one is short,
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// combine them and avoid growing the list.
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if b.canCombine(n) {
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b.blk[numStr-1].appendString(s);
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return
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}
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if cap(b.blk) == numStr {
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nstr := make([]block, numStr, 3*(numStr+10)/2);
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for i, s := range b.blk {
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nstr[i] = s;
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}
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b.blk = nstr;
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}
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b.blk = b.blk[0:numStr+1];
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// The string is immutable; no need to make a copy.
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b.blk[numStr] = (*stringBlock)(&s);
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return
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b.Truncate(0);
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}
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// Write appends the contents of p to the buffer. The return
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// value n is the length of p; err is always nil.
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func (b *Buffer) Write(p []byte) (n int, err os.Error) {
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m := b.Len();
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n = len(p);
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if n == 0 {
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return
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}
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b.len += n;
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numStr := len(b.blk);
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// Special case: If the last piece is short and this one is short,
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// combine them and avoid growing the list.
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if b.canCombine(n) {
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b.blk[numStr-1].appendBytes(p);
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return
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}
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if cap(b.blk) == numStr {
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nstr := make([]block, numStr, 3*(numStr+10)/2);
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for i, s := range b.blk {
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nstr[i] = s;
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if len(b.buf) + n > cap(b.buf) {
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// not enough space at end
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buf := b.buf;
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if m + n > cap(b.buf) {
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// not enough space anywhere
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buf = make([]byte, 2*cap(b.buf) + n)
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}
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b.blk = nstr;
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copyBytes(buf, 0, b.buf[b.off:b.off+m]);
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b.buf = buf;
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b.off = 0
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}
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b.blk = b.blk[0:numStr+1];
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// Need to copy the data - user might overwrite the data.
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b.blk[numStr] = newByteBlock(p);
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return
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b.buf = b.buf[0 : b.off + m + n];
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copyBytes(b.buf, b.off + m, p);
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return n, nil
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}
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// WriteString appends the contents of s to the buffer. The return
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// value n is the length of s; err is always nil.
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func (b *Buffer) WriteString(s string) (n int, err os.Error) {
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m := b.Len();
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n = len(s);
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if len(b.buf) + n > cap(b.buf) {
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// not enough space at end
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buf := b.buf;
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if m + n > cap(b.buf) {
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// not enough space anywhere
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buf = make([]byte, 2*cap(b.buf) + n)
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}
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copyBytes(buf, 0, b.buf[b.off:b.off+m]);
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b.buf = buf;
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b.off = 0
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}
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b.buf = b.buf[0 : b.off + m + n];
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copyString(b.buf, b.off+m, s);
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return n, nil
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}
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// WriteByte appends the byte c to the buffer.
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// The returned error is always nil, but is included
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// to match bufio.Writer's WriteByte.
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func (b *Buffer) WriteByte(c byte) os.Error {
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b.oneByte[0] = c;
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// For WriteByte, canCombine is almost always true so it's worth
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// doing here.
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if b.canCombine(1) {
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b.blk[len(b.blk)-1].appendBytes(&b.oneByte);
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b.len++;
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return nil
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if b.oneByte == nil {
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// Only happens once per Buffer, and then we have a slice.
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b.oneByte = make([]byte, 1);
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}
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b.Write(&b.oneByte);
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b.oneByte[0] = c;
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b.Write(b.oneByte);
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return nil;
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}
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@ -282,63 +133,43 @@ func (b *Buffer) WriteByte(c byte) os.Error {
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// buffer has no data to return, err is os.EOF even if len(p) is zero;
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// otherwise it is nil.
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func (b *Buffer) Read(p []byte) (n int, err os.Error) {
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if len(b.blk) == 0 {
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if b.off >= len(b.buf) {
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return 0, os.EOF
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}
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for len(b.blk) > 0 {
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blk := b.blk[0];
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m := len(p) - n;
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if l := blk.Len(); m >= l {
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// consume all of this string.
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copy(p, n, blk);
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n += l;
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b.blk = b.blk[1:len(b.blk)];
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} else {
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// consume some of this block; it's the last piece.
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switch b := blk.(type) {
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case *stringBlock:
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copyString(p, n, string(*b)[0:m]);
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case *byteBlock:
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copyBytes(p, n, []byte(*b)[0:m]);
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}
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n += m;
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b.blk[0].setSlice(m, l);
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break;
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}
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m := b.Len();
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n = len(p);
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if n > m {
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// more bytes requested than available
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n = m
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}
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b.len -= n;
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return
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copyBytes(p, 0, b.buf[b.off:b.off+n]);
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b.off += n;
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return n, err
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}
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// ReadByte reads and returns the next byte from the buffer.
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// If no byte is available, it returns error os.EOF.
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func (b *Buffer) ReadByte() (c byte, err os.Error) {
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if _, err := b.Read(&b.oneByte); err != nil {
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return 0, err
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if b.off >= len(b.buf) {
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return 0, os.EOF;
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}
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return b.oneByte[0], nil
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}
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// NewBufferString creates and initializes a new Buffer
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// using a string as its initial contents.
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func NewBufferString(str string) *Buffer {
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b := new(Buffer);
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if len(str) > 0 {
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b.blk = make([]block, 1, 10); // room to grow
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b.blk[0] = (*stringBlock)(&str);
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}
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b.len = len(str);
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return b;
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c = b.buf[b.off];
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b.off++;
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return c, nil;
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}
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// NewBuffer creates and initializes a new Buffer
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// using a byte slice as its initial contents.
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func NewBuffer(by []byte) *Buffer {
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b := new(Buffer);
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if len(by) > 0 {
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b.blk = make([]block, 1, 10); // room to grow
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b.blk[0] = (*byteBlock)(&by);
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}
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b.len = len(by);
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return b;
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// using buf as its initial contents.
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func NewBuffer(buf []byte) *Buffer {
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return &Buffer{buf: buf};
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}
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// NewBufferString creates and initializes a new Buffer
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// using string s as its initial contents.
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func NewBufferString(s string) *Buffer {
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buf := make([]byte, len(s));
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copyString(buf, 0, s);
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return &Buffer{buf: buf};
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}
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