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delphi – Invalid floating point operation calling Trunc() – Stack Overflow

Posted by jpluimers on 2021/03/18

I bumped into [WayBack] delphi – Invalid floating point operation calling Trunc() – Stack Overflow, while searching for what might have tests like these fail:

TValueRecordTests.Int64_Through_Value_Container_via_Currency_Intermediate_Is_Identity_Operation(9223372036854775807) = 9223372036854775807
EInvalidOp with message 'Invalid floating point operation'

In the end, it reproduced with a much more simple test case class of which the first three fail (EInvalidOp with message 'Invalid floating point operation'), but the last three succeed.

Lesson learned:

  • High(Int64) stored in Currency or Double, will not Trunc back to their original value.
  • Low(Int64) stored in Currency will not Trunc back to their original value.
  • Testing boundary conditions is nice, but be sure what your boundary conditions are in the first place.

unit TruncBoundariesTestsUnit;

interface

uses
  TestFramework;

type
  TTruncBoundariesTests = class(TTestCase)
  published
    procedure Trunc_Currency_High_Int64_stays_identical();
    procedure Trunc_Currency_Low_Int64_stays_identical();
    procedure Trunc_Double_High_Int64_stays_identical();
    procedure Trunc_Double_Low_Int64_stays_identical();
    procedure Trunc_Extended_High_Int64_stays_identical();
    procedure Trunc_Extended_Low_Int64_stays_identical();
  end;

implementation

procedure TTruncBoundariesTests.Trunc_Currency_High_Int64_stays_identical();
var
  Actual: Int64;
  Expected: Int64;
  Intermediate: Currency;
begin
  Expected := High(Int64);
  Intermediate := Expected;
  Actual := Trunc(Intermediate); // EInvalidOp with message 'Invalid floating point operation'
  CheckEquals(Expected, Actual);
end;

procedure TTruncBoundariesTests.Trunc_Currency_Low_Int64_stays_identical();
var
  Actual: Int64;
  Expected: Int64;
  Intermediate: Currency;
begin
  Expected := Low(Int64);
  Intermediate := Expected;
  Actual := Trunc(Intermediate); // EInvalidOp with message 'Invalid floating point operation'
  CheckEquals(Expected, Actual);
end;

procedure TTruncBoundariesTests.Trunc_Double_High_Int64_stays_identical();
var
  Actual: Int64;
  Expected: Int64;
  Intermediate: Double;
begin
  Expected := High(Int64);
  Intermediate := Expected;
  Actual := Trunc(Intermediate); // EInvalidOp with message 'Invalid floating point operation'
  CheckEquals(Expected, Actual);
end;

procedure TTruncBoundariesTests.Trunc_Double_Low_Int64_stays_identical();
var
  Actual: Int64;
  Expected: Int64;
  Intermediate: Double;
begin
  Expected := Low(Int64);
  Intermediate := Expected;
  Actual := Trunc(Intermediate);
  CheckEquals(Expected, Actual);
end;

procedure TTruncBoundariesTests.Trunc_Extended_High_Int64_stays_identical();
var
  Actual: Int64;
  Expected: Int64;
  Intermediate: Extended;
begin
  Expected := High(Int64);
  Intermediate := Expected;
  Actual := Trunc(Intermediate);
  CheckEquals(Expected, Actual);
end;

procedure TTruncBoundariesTests.Trunc_Extended_Low_Int64_stays_identical();
var
  Actual: Int64;
  Expected: Int64;
  Intermediate: Extended;
begin
  Expected := Low(Int64);
  Intermediate := Expected;
  Actual := Trunc(Intermediate);
  CheckEquals(Expected, Actual);
end;

end.

–jeroen

This entry was posted on 2021/03/18 at 06:00 and is filed under Conference Topics, Conferences, Delphi, Development, Event, Software Development. You can follow any responses to this entry through the RSS 2.0 feed. You can leave a response, or trackback from your own site.

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