Acrobat Javascript Rechenfehler

[hans-georgt40201113]

Hallo,

schwierig zu beschreiben aber vielleicht kennt jemand die Problematik zu nachstehenden vermeintlichen Rechenfehler in javascript das in einem PDF Formular eingesetzt wird.

Hier eine beispielhafte Rechnung:

1,15 - (1,15 * 0,05)

ergibt per Hand gerechnet eigentlich

1,0925

gebe ich diese Formel jedoch wie folgt als Berechnung in Acrobat ein

event.value =  1.15-(1.15*0.05)

ergibt diese Rechnung

1.0924999999999998

Frage:

Wieso werden hier Nachkommastellen eingefügt?

Wo ist hier mein Denkfehler?

Mein Problem ist, das sich dadurch Rundungsfehler im weiteren Verlauf der Berechnungen ergeben.

[try67]

This is a complex issue relating to how computer languages (and computers in general) represent floating numbers.

You can read about it more in depth here: What Every JavaScript Developer Should Know About Floating Points - Modern Web

The solution is to manually round the results to a fixed number of decimals.

You can use the toFixed method for that (although note that it returns a string, not a number), or write a function that does it using the various built-in commands of the Math object (ceil, floor, round).

[hans-georgt40201113]

thank you for the really quick answer.

my problem with round is, that my client compares my calculation with excel . The calculation they do is simply using the excel-function to round-down to the 4th dezimal.

first example:

1.325-(1.325*0.05) = 1.256375 (result excel)

1.325-(1.325*0.05) = 1.256375 (same in javascript)

excel round down is: 1.2563

javascript would do the same: 1.2563

every thing is fine!

second example:

1.15-(1.15*0.05) = 1.0925  (result excel)

1.15-(1.15*0.05) =1.0924999999999998 (result in javascript)

excel round down is: 1.0925

javascript: 1.0924

And i have no clue how to fix that.

Do you?

[try67]

For example:

(1.15-(1.15*0.05)).toFixed(4)

[hans-georgt40201113]

yup, the "funny" thing is:

(1.15-(1.15*0.05)).toFixed(4) = 1.0925

but now the result from the first example would be different from the excel one.

(1.3225-(1.3225*0.05)).toFixed(4) = 1.2564

[try67]

Yeah, that's annoying... So is Excel always rounding down? If so you'll need to write a custom function that checks the difference between your result and the nearest integer and then define a threshold to use between rounding up (in case of a floating number precision issue) or rounding down (in all other cases).

[hans-georgt40201113]

thank you for your help!

i´ll have to read a bit more about this issue. As i know now, it is a really complex thing!

have a nice day!

[try67]

If you're interested in hiring someone to do it for you feel free to contact me privately (try6767 at gmail.com). I've developed similar solution for my clients in the past.