blob: 375b38a61fbfe5c5fa697fb1fc978ef969dee2dc (
plain)
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
|
// Copyright 2016 The Draco Authors.
//
// Licensed under the Apache License, Version 2.0 (the "License");
// you may not use this file except in compliance with the License.
// You may obtain a copy of the License at
//
// http://www.apache.org/licenses/LICENSE-2.0
//
// Unless required by applicable law or agreed to in writing, software
// distributed under the License is distributed on an "AS IS" BASIS,
// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
// See the License for the specific language governing permissions and
// limitations under the License.
//
// File provides direct encoding of bits with arithmetic encoder interface.
#ifndef DRACO_COMPRESSION_BIT_CODERS_FOLDED_INTEGER_BIT_ENCODER_H_
#define DRACO_COMPRESSION_BIT_CODERS_FOLDED_INTEGER_BIT_ENCODER_H_
#include <vector>
#include "draco/core/encoder_buffer.h"
namespace draco {
// This coding scheme considers every bit of an (up to) 32bit integer as a
// separate context. This can be a significant advantage when encoding numbers
// where it is more likely that the front bits are zero.
// The behavior is essentially the same as other arithmetic encoding schemes,
// the only difference is that encoding and decoding of bits must be absolutely
// symmetric, bits handed in by EncodeBit32 must be also decoded in this way.
// This is the FoldedBit32Encoder, see also FoldedBit32Decoder.
template <class BitEncoderT>
class FoldedBit32Encoder {
public:
FoldedBit32Encoder() {}
~FoldedBit32Encoder() {}
// Must be called before any Encode* function is called.
void StartEncoding() {
for (int i = 0; i < 32; i++) {
folded_number_encoders_[i].StartEncoding();
}
bit_encoder_.StartEncoding();
}
// Encode one bit. If |bit| is true encode a 1, otherwise encode a 0.
void EncodeBit(bool bit) { bit_encoder_.EncodeBit(bit); }
// Encode |nbits| of |value|, starting from the least significant bit.
// |nbits| must be > 0 and <= 32.
void EncodeLeastSignificantBits32(int nbits, uint32_t value) {
uint32_t selector = 1 << (nbits - 1);
for (int i = 0; i < nbits; i++) {
const bool bit = (value & selector);
folded_number_encoders_[i].EncodeBit(bit);
selector = selector >> 1;
}
}
// Ends the bit encoding and stores the result into the target_buffer.
void EndEncoding(EncoderBuffer *target_buffer) {
for (int i = 0; i < 32; i++) {
folded_number_encoders_[i].EndEncoding(target_buffer);
}
bit_encoder_.EndEncoding(target_buffer);
}
private:
void Clear() {
for (int i = 0; i < 32; i++) {
folded_number_encoders_[i].Clear();
}
bit_encoder_.Clear();
}
std::array<BitEncoderT, 32> folded_number_encoders_;
BitEncoderT bit_encoder_;
};
} // namespace draco
#endif // DRACO_COMPRESSION_BIT_CODERS_FOLDED_INTEGER_BIT_ENCODER_H_
|
