usenet-indexer/lib/sevenzip/lzma.ts

/**
 * An LZMA decoder (raw stream, as a 7z coder stores it: the properties apart, the unpacked size known), after the
 * LZMA SDK's reference decoder (LzmaSpec.cpp). For 7z headers: those are small, so the whole output is one buffer.
 */

const MODEL_BITS = 11
const BIT_MODEL_TOTAL = 1 << MODEL_BITS
const MOVE_BITS = 5
const TOP = 1 << 24
const POS_BITS_MAX = 4
const STATES = 12
const LEN_TO_POS_STATES = 4
const ALIGN_BITS = 4
const END_POS_MODEL_INDEX = 14
const FULL_DISTANCES = 1 << (END_POS_MODEL_INDEX >> 1)
const MATCH_MIN_LEN = 2

export class LzmaError extends Error {}

const probs = (n: number) => new Uint16Array(n).fill(BIT_MODEL_TOTAL >>> 1)

class RangeDecoder {
  private range = 0xffffffff
  private code = 0

  constructor(
    private input: Uint8Array,
    private pos: number
  ) {
    if (this.byte() !== 0) throw new LzmaError('LZMA: bad stream start')
    for (let i = 0; i < 4; i++) this.code = ((this.code << 8) | this.byte()) >>> 0
    if (this.code === this.range) throw new LzmaError('LZMA: corrupt stream')
  }

  private byte(): number {
    if (this.pos >= this.input.length) throw new LzmaError('LZMA: input ended')
    return this.input[this.pos++]
  }

  private normalize() {
    if (this.range < TOP) {
      this.range = (this.range << 8) >>> 0
      this.code = ((this.code << 8) | this.byte()) >>> 0
    }
  }

  direct(bits: number): number {
    let result = 0
    do {
      this.range >>>= 1
      this.code = (this.code - this.range) >>> 0
      const t = this.code >>> 31 ? 0xffffffff : 0
      this.code = (this.code + (this.range & t)) >>> 0
      this.normalize()
      result = ((result << 1) | (t ? 0 : 1)) >>> 0
    } while (--bits)
    return result
  }

  bit(p: Uint16Array, i: number): number {
    const v = p[i]
    const bound = ((this.range >>> MODEL_BITS) * v) >>> 0
    let symbol: number
    if (this.code < bound) {
      p[i] = v + ((BIT_MODEL_TOTAL - v) >>> MOVE_BITS)
      this.range = bound
      symbol = 0
    } else {
      p[i] = v - (v >>> MOVE_BITS)
      this.code = (this.code - bound) >>> 0
      this.range = (this.range - bound) >>> 0
      symbol = 1
    }
    this.normalize()
    return symbol
  }

  tree(p: Uint16Array, offset: number, bits: number): number {
    let m = 1
    for (let i = 0; i < bits; i++) m = (m << 1) + this.bit(p, offset + m)
    return m - (1 << bits)
  }

  reverseTree(p: Uint16Array, offset: number, bits: number): number {
    let m = 1
    let symbol = 0
    for (let i = 0; i < bits; i++) {
      const bit = this.bit(p, offset + m)
      m = (m << 1) + bit
      symbol |= bit << i
    }
    return symbol
  }
}

class LenDecoder {
  private choice = probs(2)
  private low = probs((1 << POS_BITS_MAX) << 3)
  private mid = probs((1 << POS_BITS_MAX) << 3)
  private high = probs(1 << 8)

  decode(rc: RangeDecoder, posState: number): number {
    if (rc.bit(this.choice, 0) === 0) return rc.tree(this.low, posState << 3, 3)
    if (rc.bit(this.choice, 1) === 0) return 8 + rc.tree(this.mid, posState << 3, 3)
    return 16 + rc.tree(this.high, 0, 8)
  }
}

/** Decodes `size` bytes of a raw LZMA stream with its 5 property bytes (lc/lp/pb, dictionary size). */
export function lzmaDecode(properties: Uint8Array, input: Uint8Array, size: number): Buffer {
  if (properties.length < 5) throw new LzmaError('LZMA: short properties')
  let d = properties[0]
  if (d >= 9 * 5 * 5) throw new LzmaError('LZMA: bad properties')
  const lc = d % 9
  d = Math.floor(d / 9)
  const lp = d % 5
  const pb = Math.floor(d / 5)
  const dictSize = Math.max(properties[1] | (properties[2] << 8) | (properties[3] << 16) | (properties[4] << 24), 1 << 12) >>> 0

  const out = Buffer.alloc(size)
  let pos = 0
  const rc = new RangeDecoder(input, 0)
  const literals = probs(0x300 << (lc + lp))
  const posSlot = probs(LEN_TO_POS_STATES << 6)
  const align = probs(1 << ALIGN_BITS)
  const posDecoders = probs(1 + FULL_DISTANCES - END_POS_MODEL_INDEX)
  const isMatch = probs(STATES << POS_BITS_MAX)
  const isRep = probs(STATES)
  const isRepG0 = probs(STATES)
  const isRepG1 = probs(STATES)
  const isRepG2 = probs(STATES)
  const isRep0Long = probs(STATES << POS_BITS_MAX)
  const lenDecoder = new LenDecoder()
  const repLenDecoder = new LenDecoder()

  const distance = (len: number): number => {
    const lenState = Math.min(len, LEN_TO_POS_STATES - 1)
    const slot = rc.tree(posSlot, lenState << 6, 6)
    if (slot < 4) return slot
    const directBits = (slot >>> 1) - 1
    let dist = ((2 | (slot & 1)) * 2 ** directBits) >>> 0
    if (slot < END_POS_MODEL_INDEX) {
      dist = (dist + rc.reverseTree(posDecoders, dist - slot, directBits)) >>> 0
    } else {
      dist = (dist + rc.direct(directBits - ALIGN_BITS) * 2 ** ALIGN_BITS) >>> 0
      dist = (dist + rc.reverseTree(align, 0, ALIGN_BITS)) >>> 0
    }
    return dist
  }

  let state = 0
  let rep0 = 0
  let rep1 = 0
  let rep2 = 0
  let rep3 = 0
  while (pos < size) {
    const posState = pos & ((1 << pb) - 1)
    if (rc.bit(isMatch, (state << POS_BITS_MAX) + posState) === 0) {
      const prev = pos > 0 ? out[pos - 1] : 0
      const base = 0x300 * (((pos & ((1 << lp) - 1)) << lc) + (prev >>> (8 - lc)))
      let symbol = 1
      if (state >= 7) {
        let match = out[pos - rep0 - 1]
        do {
          const matchBit = (match >>> 7) & 1
          match <<= 1
          const bit = rc.bit(literals, base + ((1 + matchBit) << 8) + symbol)
          symbol = (symbol << 1) | bit
          if (matchBit !== bit) break
        } while (symbol < 0x100)
      }
      while (symbol < 0x100) symbol = (symbol << 1) | rc.bit(literals, base + symbol)
      out[pos++] = symbol - 0x100
      state = state < 4 ? 0 : state < 10 ? state - 3 : state - 6
      continue
    }
    let len: number
    if (rc.bit(isRep, state) !== 0) {
      if (pos === 0) throw new LzmaError('LZMA: repeat before any output')
      if (rc.bit(isRepG0, state) === 0) {
        if (rc.bit(isRep0Long, (state << POS_BITS_MAX) + posState) === 0) {
          state = state < 7 ? 9 : 11
          out[pos] = out[pos - rep0 - 1]
          pos++
          continue
        }
      } else {
        let dist: number
        if (rc.bit(isRepG1, state) === 0) {
          dist = rep1
        } else {
          if (rc.bit(isRepG2, state) === 0) {
            dist = rep2
          } else {
            dist = rep3
            rep3 = rep2
          }
          rep2 = rep1
        }
        rep1 = rep0
        rep0 = dist
      }
      len = repLenDecoder.decode(rc, posState)
      state = state < 7 ? 8 : 11
    } else {
      rep3 = rep2
      rep2 = rep1
      rep1 = rep0
      len = lenDecoder.decode(rc, posState)
      state = state < 7 ? 7 : 10
      rep0 = distance(len)
      // The end marker: allowed only where the output is complete, which the loop already ended at.
      if (rep0 === 0xffffffff) throw new LzmaError('LZMA: end marker before the end')
      if (rep0 >= dictSize || rep0 >= pos) throw new LzmaError('LZMA: distance out of range')
    }
    len += MATCH_MIN_LEN
    if (len > size - pos) throw new LzmaError('LZMA: match past the end')
    for (let i = 0; i < len; i++, pos++) out[pos] = out[pos - rep0 - 1]
  }
  return out
}