FilesExpand file tree

 master

/

ArithmeticEncoder.java

Copy path

Blame

More file actions

Blame

More file actions

Latest commit

 

History

History

History

106 lines (82 loc) · 3.25 KB

 master

/

ArithmeticEncoder.java

Copy path

Top

File metadata and controls

• Code
• Blame

106 lines (82 loc) · 3.25 KB

Raw

Copy raw file

Download raw file

Open symbols panel

Edit and raw actions

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

83

84

85

86

87

88

89

90

91

92

93

94

95

96

97

98

99

100

101

102

103

104

105

106

/*

* Reference arithmetic coding

* Copyright (c) Project Nayuki

*

* https://www.nayuki.io/page/reference-arithmetic-coding

* https://github.com/nayuki/Reference-arithmetic-coding

*/

import java.io.IOException;

import java.util.Objects;

/**

* Encodes symbols and writes to an arithmetic-coded bit stream. Not thread-safe.

* @see ArithmeticDecoder

*/

public final class ArithmeticEncoder extends ArithmeticCoderBase {

/*---- Fields ----*/

// The underlying bit output stream (not null).

private BitOutputStream output;

// Number of saved underflow bits. This value can grow without bound,

// so a truly correct implementation would use a BigInteger.

private int numUnderflow;

/*---- Constructor ----*/

/**

* Constructs an arithmetic coding encoder based on the specified bit output stream.

* @param numBits the number of bits for the arithmetic coding range

* @param out the bit output stream to write to

* @throws NullPointerException if the output stream is {@code null}

* @throws IllegalArgumentException if stateSize is outside the range [1, 62]

*/

public ArithmeticEncoder(int numBits, BitOutputStream out) {

super(numBits);

output = Objects.requireNonNull(out);

numUnderflow = 0;

}

/*---- Methods ----*/

/**

* Encodes the specified symbol based on the specified frequency table.

* This updates this arithmetic coder's state and may write out some bits.

* @param freqs the frequency table to use

* @param symbol the symbol to encode

* @throws NullPointerException if the frequency table is {@code null}

* @throws IllegalArgumentException if the symbol has zero frequency

* or the frequency table's total is too large

* @throws IOException if an I/O exception occurred

*/

public void write(FrequencyTable freqs, int symbol) throws IOException {

write(new CheckedFrequencyTable(freqs), symbol);

}

/**

* Encodes the specified symbol based on the specified frequency table.

* Also updates this arithmetic coder's state and may write out some bits.

* @param freqs the frequency table to use

* @param symbol the symbol to encode

* @throws NullPointerException if the frequency table is {@code null}

* @throws IllegalArgumentException if the symbol has zero frequency

* or the frequency table's total is too large

* @throws IOException if an I/O exception occurred

*/

public void write(CheckedFrequencyTable freqs, int symbol) throws IOException {

update(freqs, symbol);

}

/**

* Terminates the arithmetic coding by flushing any buffered bits, so that the output can be decoded properly.

* It is important that this method must be called at the end of the each encoding process.

* <p>Note that this method merely writes data to the underlying output stream but does not close it.</p>

* @throws IOException if an I/O exception occurred

*/

public void finish() throws IOException {

output.write(1);

}

protected void shift() throws IOException {

int bit = (int)(low >>> (numStateBits - 1));

output.write(bit);

// Write out the saved underflow bits

for (; numUnderflow > 0; numUnderflow--)

output.write(bit ^ 1);

}

protected void underflow() {

if (numUnderflow == Integer.MAX_VALUE)

throw new ArithmeticException("Maximum underflow reached");

numUnderflow++;

}

}