nycJSorg/angular-presentation

export function lzw(minCodeSize, data, pixelCount) {
  const MAX_STACK_SIZE = 4096;
  const nullCode = -1;

  const npix = pixelCount;
  let available,
    clear,
    code_mask,
    code_size,
    end_of_information,
    in_code,
    old_code,
    bits,
    code,
    i,
    datum,
    data_size,
    first,
    top,
    bi,
    pi;

  const dstPixels = new Array(pixelCount);
  const prefix = new Array(MAX_STACK_SIZE);
  const suffix = new Array(MAX_STACK_SIZE);
  const pixelStack = new Array(MAX_STACK_SIZE + 1);

  // Initialize GIF data stream decoder.
  data_size = minCodeSize;
  clear = 1 << data_size;
  end_of_information = clear + 1;
  available = clear + 2;
  old_code = nullCode;
  code_size = data_size + 1;
  code_mask = (1 << code_size) - 1;
  for (code = 0; code < clear; code++) {
    prefix[code] = 0;
    suffix[code] = code;
  }

  // Decode GIF pixel stream.
  datum = bits = first = top = pi = bi = 0;

  for (i = 0; i < npix; ) {
    if (top === 0) {
      if (bits < code_size) {
        // get the next byte
        datum += data[bi] << bits;

        bits += 8;
        bi++;
        continue;
      }
      // Get the next code.
      code = datum & code_mask;
      datum >>= code_size;
      bits -= code_size;
      // Interpret the code
      if (code > available || code === end_of_information) {
        break;
      }

      if (code === clear) {
        // Reset decoder.
        code_size = data_size + 1;
        code_mask = (1 << code_size) - 1;
        available = clear + 2;
        old_code = nullCode;
        continue;
      }
      if (old_code === nullCode) {
        pixelStack[top++] = suffix[code];
        old_code = code;
        first = code;
        continue;
      }
      in_code = code;
      if (code === available) {
        pixelStack[top++] = first;
        code = old_code;
      }
      while (code > clear) {
        pixelStack[top++] = suffix[code];
        code = prefix[code];
      }

      first = suffix[code] & 0xff;
      pixelStack[top++] = first;

      // add a new string to the table, but only if space is available
      // if not, just continue with current table until a clear code is found
      // (deferred clear code implementation as per GIF spec)
      if (available < MAX_STACK_SIZE) {
        prefix[available] = old_code;
        suffix[available] = first;
        available++;
        if ((available & code_mask) === 0 && available < MAX_STACK_SIZE) {
          code_size++;
          code_mask += available;
        }
      }
      old_code = in_code;
    }
    // Pop a pixel off the pixel stack.
    top--;
    dstPixels[pi++] = pixelStack[top];
    i++;
  }

  for (i = pi; i < npix; i++) {
    dstPixels[i] = 0; // clear missing pixels
  }

  return dstPixels;
}