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