SPAN_ROW_SIZE
arm = mega_mod64(stripe, SPAN_ROW_SIZE(map, ld, span));
rowMod = mega_mod64(row, SPAN_ROW_SIZE(map, ld, span));
armQ = SPAN_ROW_SIZE(map,ld,span) - 1 - rowMod;
if (arm >= SPAN_ROW_SIZE(map, ld, span))
arm -= SPAN_ROW_SIZE(map ,ld ,span);