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129 lines
3.4 KiB
129 lines
3.4 KiB
// Copyright 2014-2021 Ulrich Kunitz. 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 lzma
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import (
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"errors"
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"fmt"
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)
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// decoderDict provides the dictionary for the decoder. The whole
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// dictionary is used as reader buffer.
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type decoderDict struct {
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buf buffer
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head int64
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}
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// newDecoderDict creates a new decoder dictionary. The whole dictionary
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// will be used as reader buffer.
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func newDecoderDict(dictCap int) (d *decoderDict, err error) {
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// lower limit supports easy test cases
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if !(1 <= dictCap && int64(dictCap) <= MaxDictCap) {
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return nil, errors.New("lzma: dictCap out of range")
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}
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d = &decoderDict{buf: *newBuffer(dictCap)}
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return d, nil
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}
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// Reset clears the dictionary. The read buffer is not changed, so the
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// buffered data can still be read.
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func (d *decoderDict) Reset() {
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d.head = 0
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}
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// WriteByte writes a single byte into the dictionary. It is used to
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// write literals into the dictionary.
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func (d *decoderDict) WriteByte(c byte) error {
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if err := d.buf.WriteByte(c); err != nil {
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return err
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}
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d.head++
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return nil
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}
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// pos returns the position of the dictionary head.
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func (d *decoderDict) pos() int64 { return d.head }
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// dictLen returns the actual length of the dictionary.
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func (d *decoderDict) dictLen() int {
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capacity := d.buf.Cap()
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if d.head >= int64(capacity) {
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return capacity
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}
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return int(d.head)
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}
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// byteAt returns a byte stored in the dictionary. If the distance is
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// non-positive or exceeds the current length of the dictionary the zero
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// byte is returned.
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func (d *decoderDict) byteAt(dist int) byte {
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if !(0 < dist && dist <= d.dictLen()) {
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return 0
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}
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i := d.buf.front - dist
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if i < 0 {
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i += len(d.buf.data)
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}
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return d.buf.data[i]
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}
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// writeMatch writes the match at the top of the dictionary. The given
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// distance must point in the current dictionary and the length must not
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// exceed the maximum length 273 supported in LZMA.
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//
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// The error value ErrNoSpace indicates that no space is available in
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// the dictionary for writing. You need to read from the dictionary
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// first.
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func (d *decoderDict) writeMatch(dist int64, length int) error {
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if !(0 < dist && dist <= int64(d.dictLen())) {
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return errors.New("writeMatch: distance out of range")
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}
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if !(0 < length && length <= maxMatchLen) {
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return errors.New("writeMatch: length out of range")
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}
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if length > d.buf.Available() {
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return ErrNoSpace
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}
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d.head += int64(length)
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i := d.buf.front - int(dist)
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if i < 0 {
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i += len(d.buf.data)
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}
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for length > 0 {
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var p []byte
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if i >= d.buf.front {
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p = d.buf.data[i:]
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i = 0
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} else {
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p = d.buf.data[i:d.buf.front]
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i = d.buf.front
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}
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if len(p) > length {
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p = p[:length]
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}
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if _, err := d.buf.Write(p); err != nil {
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panic(fmt.Errorf("d.buf.Write returned error %s", err))
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}
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length -= len(p)
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}
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return nil
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}
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// Write writes the given bytes into the dictionary and advances the
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// head.
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func (d *decoderDict) Write(p []byte) (n int, err error) {
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n, err = d.buf.Write(p)
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d.head += int64(n)
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return n, err
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}
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// Available returns the number of available bytes for writing into the
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// decoder dictionary.
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func (d *decoderDict) Available() int { return d.buf.Available() }
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// Read reads data from the buffer contained in the decoder dictionary.
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func (d *decoderDict) Read(p []byte) (n int, err error) { return d.buf.Read(p) }
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