[Development] integer bug in Qt4.8.x

[Thomas Senyk]

Hi,

I think I stumbled over a bug in Qt4.8.x - QtDeclarative, but I wanted to 
asked for opinions first.

First of all: This is not happening in Qt5 (neither QtQuick2.0 nor QtQuick 
1.1)

This seems to only happen on ARM... at least I couldn't reproduce on any x86 
machine I tried.
The ARM system I tested on:
  - imx6
  - yocto based rootfs, sysroot and toolchain
  - Qt5 built using mkspecs/devices/linux-imx6-g++ (not haven the bug)
  - Qt4 built with my own mkspec based on the Qt5 device-mkspec
  - Qt4/5 source-code from git with a most recent checkout



The bug:

It's about imprecise 'int' in QtQuick1.1 / JS (only Qt4!)
A code snipped triggering it would be:

property int ex: 0

Component.onCompleted:
{
    var tmp;
    var c = 1;
    
    for ( tmp = ex + 1; /*forever*/; tmp++ )
    {
        if ( tmp !== ( ex + 1 ) )
        {
            console.log( "error: " + tmp + " != " + ex + " + 1" );
        }
        
        c = c+1;
        
        if ( c > 100000 )
        {
            console.log( tmp );
            c = 1;
        }
        
        ex = tmp;
    }
    
}


The log looks like:

...
8200000
8300000
error: 8388610 != 8388610 + 1
error: 8388612 != 8388612 + 1
error: 8388614 != 8388614 + 1
error: 8388616 != 8388616 + 1
...


where 8388610 == 0x800002

For me it looks a little bit like some sort of floating-point accuracy 
problems ... or a casting-error ... ?


Greets
Thomas