blob: cd4271193bf2e151c6a9f42dd9adb877aa8e0d82 (
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
|
// 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 providing shared functionality for RAnsSymbolEncoder and
// RAnsSymbolDecoder (see rans_symbol_encoder.h / rans_symbol_decoder.h).
#ifndef DRACO_COMPRESSION_ENTROPY_RANS_SYMBOL_CODING_H_
#define DRACO_COMPRESSION_ENTROPY_RANS_SYMBOL_CODING_H_
#include "draco/compression/entropy/ans.h"
namespace draco {
// Computes the desired precision of the rANS method for the specified number of
// unique symbols the input data (defined by their bit_length).
constexpr int ComputeRAnsUnclampedPrecision(int symbols_bit_length) {
return (3 * symbols_bit_length) / 2;
}
// Computes the desired precision clamped to guarantee a valid functionality of
// our rANS library (which is between 12 to 20 bits).
constexpr int ComputeRAnsPrecisionFromUniqueSymbolsBitLength(
int symbols_bit_length) {
return ComputeRAnsUnclampedPrecision(symbols_bit_length) < 12 ? 12
: ComputeRAnsUnclampedPrecision(symbols_bit_length) > 20
? 20
: ComputeRAnsUnclampedPrecision(symbols_bit_length);
}
// Compute approximate frequency table size needed for storing the provided
// symbols.
static inline int64_t ApproximateRAnsFrequencyTableBits(
int32_t max_value, int num_unique_symbols) {
// Approximate number of bits for storing zero frequency entries using the
// run length encoding (with max length of 64).
const int64_t table_zero_frequency_bits =
8 * (num_unique_symbols + (max_value - num_unique_symbols) / 64);
return 8 * num_unique_symbols + table_zero_frequency_bits;
}
} // namespace draco
#endif // DRACO_COMPRESSION_ENTROPY_RANS_SYMBOL_CODING_H_
|
