[GRASS-dev] How to: if undefined, set to NULL?

[Nikos Alexandris]

Nikos Alexandris:

>> Updated in sandbox, see: https://trac.osgeo.org/grass/changeset/69365
>> Is it though correct?


Vaclav Petras:
>
>I was not looking at the logic but
>
>if (hue == -1.0) {
>
>is not safe. Although it will probably work most of the time if you set it
>to the exactly same value (`hue = -1;`), but it is not portable because it
>is exact comparison for floats/doubles. Generally, you need to do something
>like
>
>if (fabs(hue - (-1.0)) < GRASS_EPSILON) {
>
>However, here it might be more appropriate to signal the good or bad state
>of hue by some other variable:
>
>hue_good = FALSE;
>
>/* setting hue here together with hue_good = TRUE */
>
>if (!hue_good) {
>
>/* do the null set */

Thanks Vaclav. Will try that out -- a quick run tells me that I didn't
understand yet how to do it. Will get to it.

>Also, it seems that the code is not consistent with FCELL versus DCELL. I
>can see DCELL *rowbuffer and Rast_is_d_null_value but also
>(FCELL)saturation as well as floats and doubles. Since the input claims to
>be always DCELL, use DCELL/double everywhere.

See my other post, if you have some time. Ideally, it would be smart to
have the input be autodetected, be it CELL or DCELL, ranging in [0,
2^bitness-of-input-data) while the output will be always FCELL (hue in
[0.0,360.0] and saturation/lightness in [0.0,1.0].

>Related to that, although I'm never sure about where is its appropriate to
>use DCELL and where double (DCELL currently gets evaluated to double:
>typedef double DCELL;). I would probably use DCELL everywhere in this
>function; just to make it clear that we deal purely with cell values and
>there is no need to switch to anything else.

But using DCELL everywhere is a bit of waisting, if I understand
correctly. I'd like to keep things clean, even if it appears to be
unnecessary to do so on first sight.

Nikos