@gmod/cram/src/rans/d04.ts

read CRAM files with pure Javascript

// @ts-nocheck
import { CramMalformedError } from '../errors.ts'
import { TF_SHIFT } from './constants.ts'
import Decoding from './decoding.ts'

export default function uncompress(
  /* ByteBuffer */ input,
  /* Decoding.AriDecoder */ D,
  /* Decoding.Symbol[] */ syms,
  /* ByteBuffer */ out,
) {
  let rans0 = input.getInt()
  let rans1 = input.getInt()
  let rans2 = input.getInt()
  let rans3 = input.getInt()

  const /* int */ outputSize = out.remaining()
  const /* int */ outputEnd = outputSize & ~3
  for (let i = 0; i < outputEnd; i += 4) {
    const /* byte */ c0 = D.R[Decoding.get(rans0, TF_SHIFT)]
    const /* byte */ c1 = D.R[Decoding.get(rans1, TF_SHIFT)]
    const /* byte */ c2 = D.R[Decoding.get(rans2, TF_SHIFT)]
    const /* byte */ c3 = D.R[Decoding.get(rans3, TF_SHIFT)]

    out.putAt(i, c0)
    out.putAt(i + 1, c1)
    out.putAt(i + 2, c2)
    out.putAt(i + 3, c3)

    rans0 = Decoding.advanceSymbolStep(rans0, syms[0xff & c0], TF_SHIFT)
    rans1 = Decoding.advanceSymbolStep(rans1, syms[0xff & c1], TF_SHIFT)
    rans2 = Decoding.advanceSymbolStep(rans2, syms[0xff & c2], TF_SHIFT)
    rans3 = Decoding.advanceSymbolStep(rans3, syms[0xff & c3], TF_SHIFT)

    rans0 = Decoding.renormalize(rans0, input)
    rans1 = Decoding.renormalize(rans1, input)
    rans2 = Decoding.renormalize(rans2, input)
    rans3 = Decoding.renormalize(rans3, input)
  }

  out.setPosition(outputEnd)
  let /* byte */ c: number
  switch (outputSize & 3) {
    case 0:
      break
    case 1:
      c = D.R[Decoding.get(rans0, TF_SHIFT)]
      Decoding.advanceSymbol(rans0, input, syms[0xff & c], TF_SHIFT)
      out.put(c)
      break

    case 2:
      c = D.R[Decoding.get(rans0, TF_SHIFT)]
      Decoding.advanceSymbol(rans0, input, syms[0xff & c], TF_SHIFT)
      out.put(c)

      c = D.R[Decoding.get(rans1, TF_SHIFT)]
      Decoding.advanceSymbol(rans1, input, syms[0xff & c], TF_SHIFT)
      out.put(c)
      break

    case 3:
      c = D.R[Decoding.get(rans0, TF_SHIFT)]
      Decoding.advanceSymbol(rans0, input, syms[0xff & c], TF_SHIFT)
      out.put(c)

      c = D.R[Decoding.get(rans1, TF_SHIFT)]
      Decoding.advanceSymbol(rans1, input, syms[0xff & c], TF_SHIFT)
      out.put(c)

      c = D.R[Decoding.get(rans2, TF_SHIFT)]
      Decoding.advanceSymbol(rans2, input, syms[0xff & c], TF_SHIFT)
      out.put(c)
      break

    default:
      throw new CramMalformedError(
        'invalid output size encountered during rANS decoding',
      )
  }

  out.setPosition(0)
}