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134 lines
3.5 KiB
134 lines
3.5 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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// treeCodec encodes or decodes values with a fixed bit size. It is using a
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// tree of probability value. The root of the tree is the most-significant bit.
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type treeCodec struct {
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probTree
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}
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// makeTreeCodec makes a tree codec. The bits value must be inside the range
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// [1,32].
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func makeTreeCodec(bits int) treeCodec {
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return treeCodec{makeProbTree(bits)}
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}
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// deepcopy initializes tc as a deep copy of the source.
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func (tc *treeCodec) deepcopy(src *treeCodec) {
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tc.probTree.deepcopy(&src.probTree)
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}
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// Encode uses the range encoder to encode a fixed-bit-size value.
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func (tc *treeCodec) Encode(e *rangeEncoder, v uint32) (err error) {
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m := uint32(1)
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for i := int(tc.bits) - 1; i >= 0; i-- {
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b := (v >> uint(i)) & 1
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if err := e.EncodeBit(b, &tc.probs[m]); err != nil {
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return err
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}
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m = (m << 1) | b
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}
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return nil
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}
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// Decodes uses the range decoder to decode a fixed-bit-size value. Errors may
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// be caused by the range decoder.
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func (tc *treeCodec) Decode(d *rangeDecoder) (v uint32, err error) {
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m := uint32(1)
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for j := 0; j < int(tc.bits); j++ {
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b, err := d.DecodeBit(&tc.probs[m])
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if err != nil {
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return 0, err
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}
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m = (m << 1) | b
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}
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return m - (1 << uint(tc.bits)), nil
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}
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// treeReverseCodec is another tree codec, where the least-significant bit is
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// the start of the probability tree.
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type treeReverseCodec struct {
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probTree
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}
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// deepcopy initializes the treeReverseCodec as a deep copy of the
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// source.
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func (tc *treeReverseCodec) deepcopy(src *treeReverseCodec) {
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tc.probTree.deepcopy(&src.probTree)
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}
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// makeTreeReverseCodec creates treeReverseCodec value. The bits argument must
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// be in the range [1,32].
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func makeTreeReverseCodec(bits int) treeReverseCodec {
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return treeReverseCodec{makeProbTree(bits)}
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}
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// Encode uses range encoder to encode a fixed-bit-size value. The range
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// encoder may cause errors.
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func (tc *treeReverseCodec) Encode(v uint32, e *rangeEncoder) (err error) {
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m := uint32(1)
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for i := uint(0); i < uint(tc.bits); i++ {
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b := (v >> i) & 1
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if err := e.EncodeBit(b, &tc.probs[m]); err != nil {
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return err
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}
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m = (m << 1) | b
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}
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return nil
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}
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// Decodes uses the range decoder to decode a fixed-bit-size value. Errors
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// returned by the range decoder will be returned.
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func (tc *treeReverseCodec) Decode(d *rangeDecoder) (v uint32, err error) {
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m := uint32(1)
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for j := uint(0); j < uint(tc.bits); j++ {
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b, err := d.DecodeBit(&tc.probs[m])
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if err != nil {
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return 0, err
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}
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m = (m << 1) | b
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v |= b << j
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}
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return v, nil
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}
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// probTree stores enough probability values to be used by the treeEncode and
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// treeDecode methods of the range coder types.
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type probTree struct {
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probs []prob
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bits byte
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}
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// deepcopy initializes the probTree value as a deep copy of the source.
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func (t *probTree) deepcopy(src *probTree) {
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if t == src {
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return
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}
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t.probs = make([]prob, len(src.probs))
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copy(t.probs, src.probs)
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t.bits = src.bits
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}
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// makeProbTree initializes a probTree structure.
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func makeProbTree(bits int) probTree {
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if !(1 <= bits && bits <= 32) {
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panic("bits outside of range [1,32]")
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}
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t := probTree{
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bits: byte(bits),
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probs: make([]prob, 1<<uint(bits)),
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}
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for i := range t.probs {
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t.probs[i] = probInit
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}
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return t
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}
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// Bits provides the number of bits for the values to de- or encode.
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func (t *probTree) Bits() int {
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return int(t.bits)
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}
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