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