Delphi date comparison

Question

What is the difference between the two functions "IsSameDay" and "SameDate" in the Delphi DateUtils library?

Answer 1

The start of the day before day zero is TDateTime(-1.0). Noon of that day is TDateTime(-1.5).

IsSameDay(-1.5, -1); // False
SameDate(-1.5, -1); // True

For positive dates, the functions are equivalent.