"Frac" function bug in Delphi?

Asked Dec 14 '16 at 19:46

Active Dec 14 '16 at 21:36

Viewed 98 times

In Delphi when I try to do this:

tmp := Frac(Frac(135.45)*100);

I see that it returns 1, when I expected 0. Why? tmp in this case is a Real variable.

Also, I used the below code to receive a visual confirmation:

Dialogs.ShowMessage(Format('Frac1=%f  Frac2=%f', [Frac(Frac(135.45)*100), Frac(45)]));

What is wrong? Is it a Delphi bug?

edited Dec 14 '16 at 21:36

Remy Lebeau

asked Dec 14 '16 at 19:46

Sergio Garcia

Probably, the actual outcome is something like `0.99999999999999999999` which output as `1`; and `0.45*100 = 44.99999999999999` – Dmitry Bychenko Dec 14 '16 at 19:49
You can check for `1.0 - tmp` to see the difference – Uwe Raabe Dec 14 '16 at 19:55
3

It's not a bug. It's an inevitable consequence of using binary floating point data types. Your number is not representable exactly. Read the answers carefully at the dupe. – David Heffernan Dec 14 '16 at 20:14
Thank you all. It's how Bychenko responds. Because it is a real number, decimal values persist and cause the error. – Sergio Garcia Dec 14 '16 at 20:19
2

There's nothing decimal here at all. It's a binary representation. – David Heffernan Dec 14 '16 at 21:04

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