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huffman.go
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/
huffman.go
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package flate
import (
"encoding/json"
"fmt"
"github.com/chronos-tachyon/huffman"
)
const (
logicalNumLLCodes = 286
logicalNumDCodes = 30
logicalNumXCodes = 15 //nolint:deadcode,varcheck
physicalNumLLCodes = 288
physicalNumDCodes = 32
physicalNumXCodes = 19
)
var scramble = [physicalNumXCodes]byte{16, 17, 18, 0, 8, 7, 9, 6, 10, 5, 11, 4, 12, 3, 13, 2, 14, 1, 15}
var (
gFixedHuffmanDecoderLL huffman.Decoder
gFixedHuffmanDecoderD huffman.Decoder
gFixedHuffmanEncoderLL huffman.Encoder
gFixedHuffmanEncoderD huffman.Encoder
)
func init() {
// https://www.rfc-editor.org/rfc/rfc1951.html - Section 3.2.6
sizes := make([]byte, physicalNumLLCodes)
for i := 0; i < 144; i++ {
sizes[i] = 8
}
for i := 144; i < 256; i++ {
sizes[i] = 9
}
for i := 256; i < 280; i++ {
sizes[i] = 7
}
for i := 280; i < 288; i++ {
sizes[i] = 8
}
if err := gFixedHuffmanDecoderLL.Init(sizes); err != nil {
panic(fmt.Errorf("failed to initialize gFixedHuffmanDecoderLL: %w", err))
}
if err := gFixedHuffmanEncoderLL.InitFromSizes(sizes); err != nil {
panic(fmt.Errorf("failed to initialize gFixedHuffmanEncoderLL: %w", err))
}
sizes = sizes[:physicalNumDCodes]
for i := 0; i < physicalNumDCodes; i++ {
sizes[i] = 5
}
if err := gFixedHuffmanDecoderD.Init(sizes); err != nil {
panic(fmt.Errorf("failed to initialize gFixedHuffmanDecoderD: %w", err))
}
if err := gFixedHuffmanEncoderD.InitFromSizes(sizes); err != nil {
panic(fmt.Errorf("failed to initialize gFixedHuffmanEncoderD: %w", err))
}
}
func getFixedHuffDecoders() (*huffman.Decoder, *huffman.Decoder) {
return &gFixedHuffmanDecoderLL, &gFixedHuffmanDecoderD
}
func getFixedHuffEncoders() (*huffman.Encoder, *huffman.Encoder) {
return &gFixedHuffmanEncoderLL, &gFixedHuffmanEncoderD
}
// SizeList represents a list of symbol sizes in a Canonical Huffman Code.
type SizeList []byte
// MarshalJSON returns the JSON representation of this SizeList, as a JSON
// Array of JSON Numbers.
func (sizelist SizeList) MarshalJSON() ([]byte, error) {
var arr []uint
if sizelist != nil {
arr = make([]uint, len(sizelist))
for index, size := range sizelist {
arr[index] = uint(size)
}
}
return json.Marshal(arr)
}