What is the equivalent of Math.Round() with MidpointRounding.AwayFromZero in Delphi?

Question

How do I use c# similar Math.Round with MidpointRounding.AwayFromZero in Delphi?

What will be the equivalent of:

double d = 2.125;
Console.WriteLine(Math.Round(d, 2, MidpointRounding.AwayFromZero));

Output: 2.13

In Delphi?

Answer 1

What you're looking for is SimpleRoundTo function in combination with SetRoundMode. As the documentations says:

SimpleRoundTo returns the nearest value that has the specified power of ten. In case AValue is exactly in the middle of the two nearest values that have the specified power of ten (above and below), this function returns:

• The value toward plus infinity if AValue is positive.

• The value toward minus infinity if AValue is negative and the FPU rounding mode is not set to rmUp

Note that the second parameter to the function is TRoundToRange which refers to exponent (power of 10) rather than number of fractional digis in .NET's Math.Round method. Therefore to round to 2 decimal places you use -2 as round-to range.

uses Math, RTTI;

var
  LRoundingMode: TRoundingMode;
begin
  for LRoundingMode := Low(TRoundingMode) to High(TRoundingMode) do
  begin
    SetRoundMode(LRoundingMode);
    Writeln(TRttiEnumerationType.GetName(LRoundingMode));
    Writeln(SimpleRoundTo(2.125, -2).ToString);
    Writeln(SimpleRoundTo(-2.125, -2).ToString);
  end;
end;

rmNearest

2,13

-2,13

rmDown

2,13

-2,13

rmUp

2,13

-2,12

rmTruncate

2,13

-2,13