vendor

vendor/github.com/ulikunitz/xz/lzma/treecodecs.go

@@ -0,0 +1,133 @@
+// 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)
+}