/* to avoid that ixs/iys is negative. this will result in bad address of pTr0/pTr1 */
vabs.s32 dPosIS, dPosIS
vmov ixs, iys, dPosIS
lsl ixs, ixs, #2
mla tmp0, srcStep, iys, ixs
add pTr0, pSrc, tmp0
add pTr1, pTr0, srcStep
in above code， tmp0 maybe more than imgWidethimgHeight4