Re: [Mingw-users] MinGW and Floating Point

[Steve C. <ste...@gm...>]

On 06/04/2010 12:36 PM, Richard C. Wagner wrote:
> Kein-Hong and Ben,
>
> Thanks for your responses.  Kein-Hong wrote:
>
>    
>> A float has about 7 decimal digits of precision. For whatever
>> reasons, your result has a 1 plus 'a very small number'. So,
>> taking 8 digits of displayed result (since the '1' at the front
>> doesn't 'contribute' a full 1 digits of precision):
>>
>> 1.0000014
>> 1.0000015
>> 1.0000017
>>
>> Nothing wrong with the compiler or the machine.
>>      
> and Ben added:
>
>    
>> There is something very wrong somewhere because if you are performing
>>
>> x / 640.0 *  9e-6
>>
>> For 0.0<= x<= 640.0
>>
>> Your results should be way less than 1.
>>      
> Then Kein-Hong correctly deduced:
>
>    
>> Sounds like a throwaway test of some sort when zooming in failed
>> (or turned blocky) due to lack of numeric precision.
>>      
>
> Sorry, my description of my test wasn't clear.  The results I posted were
> from a stand-alone, throw away test program that made the same calculation
> that I'm using in my main program.  The calculation is:
>
> Domain_x = ((Pixel_x / 640.0) * 9.0e-6) + 1.0
>
>    
I've found that the problem is usually in the source code that *isn't* 
shown. Could you post a complete, self-contained, short program that 
illustrates the problem?