1// Copyright 2014-2017 Ulrich Kunitz. All rights reserved.
2// Use of this source code is governed by a BSD-style
3// license that can be found in the LICENSE file.
4
5package lzma
6
7import "fmt"
8
9// directCodec allows the encoding and decoding of values with a fixed number
10// of bits. The number of bits must be in the range [1,32].
11type directCodec byte
12
13// makeDirectCodec creates a directCodec. The function panics if the number of
14// bits is not in the range [1,32].
15func makeDirectCodec(bits int) directCodec {
16	if !(1 <= bits && bits <= 32) {
17		panic(fmt.Errorf("bits=%d out of range", bits))
18	}
19	return directCodec(bits)
20}
21
22// Bits returns the number of bits supported by this codec.
23func (dc directCodec) Bits() int {
24	return int(dc)
25}
26
27// Encode uses the range encoder to encode a value with the fixed number of
28// bits. The most-significant bit is encoded first.
29func (dc directCodec) Encode(e *rangeEncoder, v uint32) error {
30	for i := int(dc) - 1; i >= 0; i-- {
31		if err := e.DirectEncodeBit(v >> uint(i)); err != nil {
32			return err
33		}
34	}
35	return nil
36}
37
38// Decode uses the range decoder to decode a value with the given number of
39// given bits. The most-significant bit is decoded first.
40func (dc directCodec) Decode(d *rangeDecoder) (v uint32, err error) {
41	for i := int(dc) - 1; i >= 0; i-- {
42		x, err := d.DirectDecodeBit()
43		if err != nil {
44			return 0, err
45		}
46		v = (v << 1) | x
47	}
48	return v, nil
49}
50