134 lines
3.5 KiB
Go
134 lines
3.5 KiB
Go
// Copyright 2014-2017 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)
|
|
}
|