Diff

Differences From Artifact [f2ad12a795]:

To Artifact [cebf1719c8]:


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
107
108
109
110
111
112
113
114
115
116
117
118
119
120

121
122
123
	240, 241, 242, 243, 244, 245, 246, 247, 248, 249, 250, 251, 252, 253, 254, 255,
}

type context struct {
	table [256]byte
}

// Returns an MTF encoder over the provided io.Writer
func Encoder(writer io.Writer) io.Writer {
	var enc encoder
	enc.table = initial
	enc.target = writer
	return &enc
}

type encoder struct {
	context
	target io.Writer
}

func (c *encoder) Write(data []byte) (int, error) {
	var (
		dataLength int    = len(data)
		buffer     []byte = make([]byte, dataLength)
	)

	// io.Write must not modify the passed data in any way
	// TODO - check sync.Pool or a local free-list for amortizing buffers
	// TODO - use a buffer with a fixed max size to avoid OOM conditions

	// Loop over the input data
	for index, value := range data {

		// Shortcut for sequential, equal values
		if c.table[0] == value {
			buffer[index] = 0
			continue
		}

		// Loop over the MTF table
		for j := byte(1); j != 0; j++ {
			if c.table[j] == value {
				// Output the value
				buffer[index] = j

				// Shift the table
				copy(c.table[1:], c.table[:j])

				// Restore the value in front and break
				c.table[0] = value
				break
			}
		}
	}

	return c.target.Write(buffer)
}









































// Returns an MTF decoder over the provided io.Writer
func Decoder(reader io.Reader) io.Reader {
	var dec decoder
	dec.table = initial
	dec.source = reader
	return &dec
}

type decoder struct {
	context
	source io.Reader
}


func (c *decoder) Read(output []byte) (int, error) {
	var (
		count    int
		err      error
		position byte
	)

	// Read from the source and decode in place
	count, err = c.source.Read(output)
	for i := 0; i < count; i++ {
		position = output[i]

		// Shortcut for sequential, equal values
		if position == 0 {
			output[i] = c.table[0]
			continue
		}

		// Output the value
		output[i] = c.table[position]

		// Shift the table and restore the value in front
		copy(c.table[1:], c.table[:position])
		c.table[0] = output[i]
	}


	return count, err
}







|
|
<
<
<
<
<
<
<
<
<
<
<
<
<
<
<
<
<
<
<
<
<
<




|







|










|
<
|
>
>
>
>

>
>
>
>
>
>
>
>
>
>
>
>
>
>
>
>
>
>
>
>
>
>
>
>
>
>
>
>
>
>
>
>
>
>
>
>
|












>
|
<
<
<
<
<
<
<

<
<
<
<
<
<
<
<
<
<
<
<
<
<
<
<
>



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
107
108
109
110
111
112
113
114







115
















116
117
118
119
	240, 241, 242, 243, 244, 245, 246, 247, 248, 249, 250, 251, 252, 253, 254, 255,
}

type context struct {
	table [256]byte
}

// Encodes data in place
func (c *context) encode(data []byte) {






















	for index, value := range data {

		// Shortcut for sequential, equal values
		if c.table[0] == value {
			data[index] = 0
			continue
		}

		// Loop over the MTF table
		for j := byte(1); j != 0; j++ {
			if c.table[j] == value {
				// Output the value
				data[index] = j

				// Shift the table
				copy(c.table[1:], c.table[:j])

				// Restore the value in front and break
				c.table[0] = value
				break
			}
		}
	}
}


// Decode data in place
func (c *context) decode(data []byte) {
	for index, value := range data {
		position := value

		// Shortcut for sequential, equal values
		if position == 0 {
			data[index] = c.table[0]
			continue
		}

		// Output the value
		data[index] = c.table[position]

		// Shift the table and restore the value in front
		copy(c.table[1:], c.table[:position])
		c.table[0] = data[index]
	}
}

// Returns an MTF encoder over the provided io.Reader
func Encoder(reader io.Reader) io.Reader {
	var enc encoder
	enc.table = initial
	enc.source = reader
	return &enc
}

type encoder struct {
	context
	source io.Reader
}

// Read and encode data in place
func (c *encoder) Read(output []byte) (count int, err error) {
	count, err = c.source.Read(output)
	c.encode(output[:count])

	return count, err
}

// Returns an MTF decoder over the provided io.Reader
func Decoder(reader io.Reader) io.Reader {
	var dec decoder
	dec.table = initial
	dec.source = reader
	return &dec
}

type decoder struct {
	context
	source io.Reader
}

// Read and decode data in place
func (c *decoder) Read(output []byte) (count int, err error) {







	count, err = c.source.Read(output)
















	c.decode(output[:count])

	return count, err
}