ROUND_CEILING:
Move towards positive infinity when rounding 1.1->2 1.5->2 1.8->2 -1.1->-1 -1.5->-1 -1.8->-1
ROUND_DOWN:
Move towards 0 by 1.1->1 1.5->1 1.8->1 -1.1->-1 -1.5->-1 -1.8>-1
ROUND_FLOOR:
Contrary to CEILING, towards negative infinity 1.1->1 1.5->1 1.8->1 -1.1->-2 -1.5->-2 -1.8->-2
ROUND_HALF_DOWN:
Take 5 as the dividing line, or round up 1.5->1 1.6->1 -1.5->-1 -1.6->-2 1.15->1.1 1.16->1.2 1.55->1.6 1.56->1.6 ROUND_HALF_EVEN
:
Also use 5 as the dividing line. If it is 5, the previous digit becomes an even number 1.15->1.2 1.16->1.2 1.25->1.2 1.26->1.3
ROUND_HALF_UP:
The most common rounding
ROUND_UNNECESSARY:
Without rounding
ROUND_UP:
With ROUND_DOWN, the directions away from 0 are 1.1->2 1.5->2 1.8->2 -1.1->-2 -1.5->-2 -1.8->-2