[postgis-devel] [wktraster] Core tests failure for r5841

[Jorge Arévalo]

On Thu, Jan 13, 2011 at 10:08 AM, strk <strk at keybit.net> wrote:
> On Thu, Jan 13, 2011 at 01:12:58AM +0000, Mateusz Loskot wrote:
>
>> "Something must have gone wrong on Mat`s one" means either GCC team has
>> screwed their compiler and it generates rubbish, or we have problem in
>> PostGIS. Which one you vote for?
>
> Hey...
> We're talking about a message of this form:
>
>  WARNING:  Initial pixel value for 16BSI band got truncated from XXX to YYY
>
> Sounds like the problem isn't going unnoticed, which is good.
> That's all that test is checking: if numbers that don't fit in 16BSI
> representation are correctly WARNED about.
>
> I vote for "a problem with testing framework" :)
>
> --strk;
>
>  ()   Free GIS & Flash consultant/developer
>  /\   http://strk.keybit.net/services.html
> _______________________________________________
> postgis-devel mailing list
> postgis-devel at postgis.refractions.net
> http://postgis.refractions.net/mailman/listinfo/postgis-devel
>

Mmmm... Mateusz is right. In case of 210000.46, for example. When you
cast from double to uint16:

1.- First, discard decimal part --> 210000
2.- Convert the real part to integer

210000 = 0b110011010001010000

If you get the 16 LSB --> 0b0011010001010000 = 13392

But if, as the standard says, there's UB with these casts, how should
we write a test?

Best regards,
-- 
Jorge Arévalo
Internet & Mobilty Division, DEIMOS
jorge.arevalo at deimos-space.com
http://mobility.grupodeimos.com/
http://gis4free.wordpress.com
http://geohash.org/ezjqgrgzz0g