pRawx      = pData->pWorkrow + 1 + iBpp; pRawx_prev = pData->pWorkrow + 1;
pRawx      = pData->pWorkrow + pData->iPixelofs + iBpp; pRawx_prev = pData->pWorkrow + pData->iPixelofs;
mng_retcode filter_sub (mng_datap pData){  mng_uint32 iBpp;  mng_uint8p pRawx;  mng_uint8p pRawx_prev;  mng_int32  iX;#ifdef MNG_SUPPORT_TRACE  MNG_TRACE (pData, MNG_FN_FILTER_SUB, MNG_LC_START)#endif  iBpp       = pData->iFilterbpp;  pRawx      = pData->pWorkrow + 1 + iBpp;  pRawx_prev = pData->pWorkrow + 1;  for (iX = iBpp; iX < pData->iRowsize; iX++)  {    pRawx [0] = (mng_uint8)(pRawx [0] + pRawx_prev [0]);    pRawx++;    pRawx_prev++;  }#ifdef MNG_SUPPORT_TRACE  MNG_TRACE (pData, MNG_FN_FILTER_SUB, MNG_LC_END)#endif  return MNG_NOERROR;}