Strange behavior or a bug in Autoit - Neither!

[Guest]

Hi,

I think that this is a bug:

$iMax = 14/5
$iMax = $iMax-Int($iMax)
$iMax *= 5

ConsoleWrite("$iMax is: "&$iMax & @CRLF&@CRLF) ; Print $iMax as 4


; Bug 1: this will end at 3 while $iMax is 4!
ConsoleWrite("Starting loop from 1 to "&$iMax&":" & @CRLF)
For $a = 1 To $iMax
    ConsoleWrite($a & @CRLF)
Next
ConsoleWrite("Done!" & @CRLF & @CRLF)



; Bug 2: the array will be with 3 rows and not 4.
ConsoleWrite("Creating array with "&$iMax&" rows:" & @CRLF)
Local $aArray[$iMax+1]
ConsoleWrite("array size: "& UBound($aArray)-1 & @CRLF)

 

 

Output:

Quote

$iMax is: 4

Starting loop from 1 to 4:
1
2
3
Done!

Creating array with 4 rows:
array size: 3

Runned on Autoit 3.3.14.2

 

If that's not a bug, I really, really want to know what is the explanation for this very unexpected behavior.

 

 

Edited February 2, 2016 by Guest
Amended title

[BrewManNH]

When doing floating point math, the numbers aren't exactly what they appear to be.

Try this modification:

$iMax = Int($iMax*5)

Now you'll get what you want.

[UEZ]

The problem is that $iMax is "double".

$iMax = 14 / 5
$iMax = $iMax - Int($iMax)
$iMax = $iMax * 5

ConsoleWrite(VarGetType($iMax) & @CRLF)

$iMax = Int($iMax)

ConsoleWrite("$iMax is: " & $iMax & @CRLF & @CRLF) ; Print $iMax as 4


; Bug 1: this will end at 3 while $iMax is 4!
ConsoleWrite("Starting loop from 1 to " & $iMax & ":" & @CRLF)
For $a = 1 To $iMax
    ConsoleWrite($a & @CRLF)
Next
ConsoleWrite("Done" & @CRLF & @CRLF)



; Bug 2: the array will be with 3 rows and not 4.
ConsoleWrite("Creating array with " & $iMax & " rows:" & @CRLF)
Local $aArray[$iMax + 1]
ConsoleWrite("array size: " & UBound($aArray) - 1 & @CRLF)

 

Edited January 28, 2016 by UEZ

[Guest]

15 minutes ago, BrewManNH said:

When doing floating point math, the numbers aren't exactly what they appear to be.

Try this modification:

$iMax = Int($iMax*5)

Now you'll get what you want.

 

 

Yes,
I noticed that the "bug" only happens if I get $iMax with this kind of math. I just started to learn c++ and this scenario has taught me something new.

but I didn't expected to learn it from Autoit..

 

From what I understand about how Autoit should work on paper by  design, It should work as normal person can expect (4 is 4 and not 3). and not work like tricky language like C.

according to this view, this is bug. - I mean, If Autoit was C so ok, this is not bug. but it is Autoit. so this is bug...

 

 

Edited January 28, 2016 by Guest

[UEZ]

What I cannot understand is why these are different results:

$iMax = 14 / 5
$iMax = $iMax - Int($iMax)
$iMax = $iMax * 5.0 ;result should be 4.0

ConsoleWrite("$iMax is: " & $iMax & @CRLF & @CRLF) ; Print $iMax as 4

; Bug 1: this will end at 3 while $iMax is 4!
ConsoleWrite("Starting loop from 1 to " & $iMax & ":" & @CRLF)
ConsoleWrite(VarGetType($iMax) & @CRLF)
For $a = 1 To $iMax
    ConsoleWrite($a & @CRLF)
Next
ConsoleWrite(@CRLF)

ConsoleWrite(VarGetType(4.0) & @CRLF)
For $a = 1 To 4.0
    ConsoleWrite($a & @CRLF)
Next
ConsoleWrite("Done" & @CRLF & @CRLF)

Shouldn't be the same result? 

 

Edit:

Seems to be that $iMax <> 4.0 internally.

$iMax = 14 / 5
$iMax = $iMax - Int($iMax)
$iMax = $iMax * 5.0

ConsoleWrite(Hex($iMax) & @CRLF)
ConsoleWrite(Hex(4.0) & @CRLF)

Result is:

400FFFFFFFFFFFFE
4010000000000000

 

That could be the reason for the different result.

Edited January 28, 2016 by UEZ

[Guest]

12 minutes ago, UEZ said:

What I cannot understand is why these are different results:

$iMax = 14 / 5
$iMax = $iMax - Int($iMax)
$iMax = $iMax * 5.0 ;result should be 4.0

ConsoleWrite("$iMax is: " & $iMax & @CRLF & @CRLF) ; Print $iMax as 4

; Bug 1: this will end at 3 while $iMax is 4!
ConsoleWrite("Starting loop from 1 to " & $iMax & ":" & @CRLF)
ConsoleWrite(VarGetType($iMax) & @CRLF)
For $a = 1 To $iMax
    ConsoleWrite($a & @CRLF)
Next
ConsoleWrite(@CRLF)

ConsoleWrite(VarGetType(4.0) & @CRLF)
For $a = 1 To 4.0
    ConsoleWrite($a & @CRLF)
Next
ConsoleWrite("Done" & @CRLF & @CRLF)

Shouldn't be the same result? 

According to this, that fact that it is Double may not the be cause for this behavior.

 

Maybe there is really bug here (I just don't know where exactly)

 

[iamtheky]

the 15th decimal place jacks you every time   If I understood anything at all about floating points I could tell you why changing the 14 to a 15 breaks it.

$iMax = 14/5
$iMax = $iMax - Int($iMax)
$iMax = round($iMax * 5 , 14)

ConsoleWrite("$iMax is: "&$iMax & @CRLF&@CRLF) ; Print $iMax as 4


; Bug 1: this will end at 3 while $iMax is 4!
ConsoleWrite("Starting loop from 1 to "&$iMax&":" & @CRLF)
For $a = 1 To $iMax
    ConsoleWrite($a & @CRLF)
Next
ConsoleWrite("Done!" & @CRLF & @CRLF)



; Bug 2: the array will be with 3 rows and not 4.
ConsoleWrite("Creating array with "&$iMax&" rows:" & @CRLF)
Local $aArray[$iMax+1]
ConsoleWrite("array size: "& UBound($aArray)-1 & @CRLF)

 

[jpm]

just because float has only 14 sure digit precision

[Bowmore]

This might help you understand

$dMax = 14/5
ConsoleWrite("$dMax is: "&StringFormat("%0.20f",$dMax) & @CRLF&@CRLF) ;
$dMax = $dMax-Int($dMax)
ConsoleWrite("$dMax is: "&StringFormat("%0.20f",$dMax) & @CRLF&@CRLF) ;

$dMax *= 5

; Bug 1: this will end at 3 while $iMax is 4!
ConsoleWrite("Starting loop from 1 to "&StringFormat("%0.20f",$dMax)&":" & @CRLF)
For $a = 1 To $dMax
    ConsoleWrite($a & @CRLF)
Next
ConsoleWrite("Done!" & @CRLF & @CRLF)

$iMax = Round($dMax)
ConsoleWrite("Starting loop from 1 to "&StringFormat("%0.20f",$iMax)&":" & @CRLF)
For $a = 1 To $iMax
    ConsoleWrite($a & @CRLF)
Next
ConsoleWrite("Done!" & @CRLF & @CRLF)


; Bug 2: the array will be with 3 rows and not 4.
ConsoleWrite("Creating array with "&$iMax&" rows:" & @CRLF)
Local $aArray[$iMax+1]
ConsoleWrite("array size: "& UBound($aArray)-1 & @CRLF)

 

Edited January 28, 2016 by Bowmore

[Guest]

1 hour ago, Bowmore said:

This might help you understand

$dMax = 14/5
ConsoleWrite("$dMax is: "&StringFormat("%0.20f",$dMax) & @CRLF&@CRLF) ;
$dMax = $dMax-Int($dMax)
ConsoleWrite("$dMax is: "&StringFormat("%0.20f",$dMax) & @CRLF&@CRLF) ;

$dMax *= 5

; Bug 1: this will end at 3 while $iMax is 4!
ConsoleWrite("Starting loop from 1 to "&StringFormat("%0.20f",$dMax)&":" & @CRLF)
For $a = 1 To $dMax
    ConsoleWrite($a & @CRLF)
Next
ConsoleWrite("Done!" & @CRLF & @CRLF)

$iMax = Round($dMax)
ConsoleWrite("Starting loop from 1 to "&StringFormat("%0.20f",$iMax)&":" & @CRLF)
For $a = 1 To $iMax
    ConsoleWrite($a & @CRLF)
Next
ConsoleWrite("Done!" & @CRLF & @CRLF)


; Bug 2: the array will be with 3 rows and not 4.
ConsoleWrite("Creating array with "&$iMax&" rows:" & @CRLF)
Local $aArray[$iMax+1]
ConsoleWrite("array size: "& UBound($aArray)-1 & @CRLF)

 

Thanks.

Now it make make sense.

But why 14/5 is 2.79999999999999980000 ?

And why it didn't choose to display this number in the console?

 

I tested it now on C++ and got the same behavor

#include "stdafx.h"
#include <iostream>
#include <windows.h>
using namespace std;
int main()
{
    float x = 14.0 / 5.0;
    x -= int(x);
    x *= 5;

    cout << "Starting loop from 1 to " << x << endl;
    for (int i = 1; i <= x; i++)
    {
        cout << i << endl;
    }
    while (1) { Sleep(100); }
    return 1;
}

 

[AndyG]

http://www.plantation-productions.com/Webster/www.artofasm.com/Linux/HTML/RealArithmetic.html

Depending of setting the Rounding-control Register different results are to be expected. 

From time to time I write programs in assembler, and a long time ago i noticed different results comparing floating-point math calculations to AutoIt! The cause is that AutoIt uses Windows-API-Functions where the registersettings are established since decades....

Setting those Control-Registers "in the right way" (the usually used way from the sight of a Programmer) gives me "right" (equal to AutoIt-Calculations) results...

People have to notice,  that today there is no need to have  "right" results when calculating floating-point math! The most important thing is, that the results are EQUAL when calculating those maths on different machines!

With this informations in mind there is a simple trick to solve those problems. Trust the API, not your brain... so there exist no "bugs" when the result is the same on other machines too...

 

This is the way i set control-register to get equal results to AutoIt when calculating Floating-point math: (like C/C++/HLL does since decades  )

finit

    fstcw ctrlWord
    and ctrlWord, 000000111111b                           ;bit 8+9 ;53 Bit genauigkeit, um Kompatibilität zu AutoIt zu erreichen
    or ctrlWord,  001000000000b                           ;bit 10+11 abrunden wg INT
    fldcw ctrlWord

 

 

 

But why 14/5 is 2.79999999999999980000 ?

IEEE 754 Converter, have a look at the line "after casting to double precision"

http://www.h-schmidt.net/FloatConverter/IEEE754.html

Edited January 30, 2016 by AndyG

[czardas]

Use Fraction.au3 and never have to worry about this kind of problem ever again. 2c