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gitea/vendor/github.com/nwaples/rardecode/huffman.go

208 lines
3.9 KiB

package rardecode
import (
"errors"
"io"
)
const (
maxCodeLength = 15 // maximum code length in bits
maxQuickBits = 10
maxQuickSize = 1 << maxQuickBits
)
var (
errHuffDecodeFailed = errors.New("rardecode: huffman decode failed")
errInvalidLengthTable = errors.New("rardecode: invalid huffman code length table")
)
type huffmanDecoder struct {
limit [maxCodeLength + 1]int
pos [maxCodeLength + 1]int
symbol []int
min uint
quickbits uint
quicklen [maxQuickSize]uint
quicksym [maxQuickSize]int
}
func (h *huffmanDecoder) init(codeLengths []byte) {
var count [maxCodeLength + 1]int
for _, n := range codeLengths {
if n == 0 {
continue
}
count[n]++
}
h.pos[0] = 0
h.limit[0] = 0
h.min = 0
for i := uint(1); i <= maxCodeLength; i++ {
h.limit[i] = h.limit[i-1] + count[i]<<(maxCodeLength-i)
h.pos[i] = h.pos[i-1] + count[i-1]
if h.min == 0 && h.limit[i] > 0 {
h.min = i
}
}
if cap(h.symbol) >= len(codeLengths) {
h.symbol = h.symbol[:len(codeLengths)]
for i := range h.symbol {
h.symbol[i] = 0
}
} else {
h.symbol = make([]int, len(codeLengths))
}
copy(count[:], h.pos[:])
for i, n := range codeLengths {
if n != 0 {
h.symbol[count[n]] = i
count[n]++
}
}
if len(codeLengths) >= 298 {
h.quickbits = maxQuickBits
} else {
h.quickbits = maxQuickBits - 3
}
bits := uint(1)
for i := 0; i < 1<<h.quickbits; i++ {
v := i << (maxCodeLength - h.quickbits)
for v >= h.limit[bits] && bits < maxCodeLength {
bits++
}
h.quicklen[i] = bits
dist := v - h.limit[bits-1]
dist >>= (maxCodeLength - bits)
pos := h.pos[bits] + dist
if pos < len(h.symbol) {
h.quicksym[i] = h.symbol[pos]
} else {
h.quicksym[i] = 0
}
}
}
func (h *huffmanDecoder) readSym(r bitReader) (int, error) {
bits := uint(maxCodeLength)
v, err := r.readBits(maxCodeLength)
if err != nil {
if err != io.EOF {
return 0, err
}
// fall back to 1 bit at a time if we read past EOF
for i := uint(1); i <= maxCodeLength; i++ {
b, err := r.readBits(1)
if err != nil {
return 0, err // not enough bits return error
}
v |= b << (maxCodeLength - i)
if v < h.limit[i] {
bits = i
break
}
}
} else {
if v < h.limit[h.quickbits] {
i := v >> (maxCodeLength - h.quickbits)
r.unreadBits(maxCodeLength - h.quicklen[i])
return h.quicksym[i], nil
}
for i, n := range h.limit[h.min:] {
if v < n {
bits = h.min + uint(i)
r.unreadBits(maxCodeLength - bits)
break
}
}
}
dist := v - h.limit[bits-1]
dist >>= maxCodeLength - bits
pos := h.pos[bits] + dist
if pos > len(h.symbol) {
return 0, errHuffDecodeFailed
}
return h.symbol[pos], nil
}
// readCodeLengthTable reads a new code length table into codeLength from br.
// If addOld is set the old table is added to the new one.
func readCodeLengthTable(br bitReader, codeLength []byte, addOld bool) error {
var bitlength [20]byte
for i := 0; i < len(bitlength); i++ {
n, err := br.readBits(4)
if err != nil {
return err
}
if n == 0xf {
cnt, err := br.readBits(4)
if err != nil {
return err
}
if cnt > 0 {
// array already zero'd dont need to explicitly set
i += cnt + 1
continue
}
}
bitlength[i] = byte(n)
}
var bl huffmanDecoder
bl.init(bitlength[:])
for i := 0; i < len(codeLength); i++ {
l, err := bl.readSym(br)
if err != nil {
return err
}
if l < 16 {
if addOld {
codeLength[i] = (codeLength[i] + byte(l)) & 0xf
} else {
codeLength[i] = byte(l)
}
continue
}
var count int
var value byte
switch l {
case 16, 18:
count, err = br.readBits(3)
count += 3
default:
count, err = br.readBits(7)
count += 11
}
if err != nil {
return err
}
if l < 18 {
if i == 0 {
return errInvalidLengthTable
}
value = codeLength[i-1]
}
for ; count > 0 && i < len(codeLength); i++ {
codeLength[i] = value
count--
}
i--
}
return nil
}