unsigned lodepng_inspect(unsigned* w, unsigned* h, LodePNGState* state,
                         const unsigned char* in, size_t insize)
{
  LodePNGInfo* info = &state->info_png;
  if(insize == 0 || in == 0)
  {
    CERROR_RETURN_ERROR(state->error, 48); /*error: the given data is empty*/
  }
  if(insize < 29)
  {
    CERROR_RETURN_ERROR(state->error, 27); /*error: the data length is smaller than the length of a PNG header*/
  }

  /*when decoding a new PNG image, make sure all parameters created after previous decoding are reset*/
  lodepng_info_cleanup(info);
  lodepng_info_init(info);

  if(in[0] != 137 || in[1] != 80 || in[2] != 78 || in[3] != 71
     || in[4] != 13 || in[5] != 10 || in[6] != 26 || in[7] != 10)
  {
    CERROR_RETURN_ERROR(state->error, 28); /*error: the first 8 bytes are not the correct PNG signature*/
  }
  if(in[12] != 'I' || in[13] != 'H' || in[14] != 'D' || in[15] != 'R')
  {
    CERROR_RETURN_ERROR(state->error, 29); /*error: it doesn't start with a IHDR chunk!*/
  }

  /*read the values given in the header*/
  *w = lodepng_read32bitInt(&in[16]);
  *h = lodepng_read32bitInt(&in[20]);
  info->color.bitdepth = in[24];
  info->color.colortype = (LodePNGColorType)in[25];
  info->compression_method = in[26];
  info->filter_method = in[27];
  info->interlace_method = in[28];

  if(!state->decoder.ignore_crc)
  {
    unsigned CRC = lodepng_read32bitInt(&in[29]);
    unsigned checksum = lodepng_crc32(&in[12], 17);
    if(CRC != checksum)
    {
      CERROR_RETURN_ERROR(state->error, 57); /*invalid CRC*/
    }
  }

  /*error: only compression method 0 is allowed in the specification*/
  if(info->compression_method != 0) CERROR_RETURN_ERROR(state->error, 32);
  /*error: only filter method 0 is allowed in the specification*/
  if(info->filter_method != 0) CERROR_RETURN_ERROR(state->error, 33);
  /*error: only interlace methods 0 and 1 exist in the specification*/
  if(info->interlace_method > 1) CERROR_RETURN_ERROR(state->error, 34);

  state->error = checkColorValidity(info->color.colortype, info->color.bitdepth);
  return state->error;
}
Unknown