mirror of https://github.com/golang/go.git
91 lines
2.0 KiB
Go
91 lines
2.0 KiB
Go
// Copyright 2023 The Go Authors. All rights reserved.
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// Use of this source code is governed by a BSD-style
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// license that can be found in the LICENSE file.
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package zstd
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// window stores up to size bytes of data.
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// It is implemented as a circular buffer:
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// sequential save calls append to the data slice until
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// its length reaches configured size and after that,
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// save calls overwrite previously saved data at off
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// and update off such that it always points at
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// the byte stored before others.
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type window struct {
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size int
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data []byte
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off int
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}
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// reset clears stored data and configures window size.
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func (w *window) reset(size int) {
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w.data = w.data[:0]
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w.off = 0
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w.size = size
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}
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// len returns the number of stored bytes.
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func (w *window) len() uint32 {
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return uint32(len(w.data))
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}
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// save stores up to size last bytes from the buf.
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func (w *window) save(buf []byte) {
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if w.size == 0 {
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return
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}
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if len(buf) == 0 {
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return
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}
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if len(buf) >= w.size {
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from := len(buf) - w.size
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w.data = append(w.data[:0], buf[from:]...)
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w.off = 0
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return
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}
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// Update off to point to the oldest remaining byte.
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free := w.size - len(w.data)
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if free == 0 {
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n := copy(w.data[w.off:], buf)
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if n == len(buf) {
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w.off += n
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} else {
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w.off = copy(w.data, buf[n:])
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}
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} else {
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if free >= len(buf) {
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w.data = append(w.data, buf...)
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} else {
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w.data = append(w.data, buf[:free]...)
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w.off = copy(w.data, buf[free:])
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}
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}
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}
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// appendTo appends stored bytes between from and to indices to the buf.
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// Index from must be less or equal to index to and to must be less or equal to w.len().
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func (w *window) appendTo(buf []byte, from, to uint32) []byte {
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dataLen := uint32(len(w.data))
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from += uint32(w.off)
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to += uint32(w.off)
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wrap := false
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if from > dataLen {
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from -= dataLen
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wrap = !wrap
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}
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if to > dataLen {
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to -= dataLen
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wrap = !wrap
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}
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if wrap {
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buf = append(buf, w.data[from:]...)
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return append(buf, w.data[:to]...)
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} else {
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return append(buf, w.data[from:to]...)
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}
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}
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