Floor and CEIL are functions in Math Unit, and you must first use Uses Math before use.
Trunc and Round are functions in the System Unit, which is available in default.
FLOOR directly takes a small, such as floor (-123.55) = - 124, floor (123.55) = 123
Trunc cuts an integer, such as trunc (-123.55) = - 123, floor (123.55) = 123
CEIL is directly taken, such as CEIL (-123.55) = - 123, CEIL (123.55) = 124
Round calculation is rounded, such as ROUND (-123.55) = - 124, Round (123.55) = 124
