[GRASS-dev] r.mapcal rand() strangeness

[Maciej Sieczka]

Maciej Sieczka pisze:
> Maciej Sieczka pisze:
>> Glynn Clements pisze:
>>> Maciej Sieczka wrote:

>>>> $ r.mapcalc 'map=rand(-2147483648,2147483647)'

>>>     res[i] = (lo == hi) ? lo : lo + x % (hi - lo);
>>>
>>> The expression (hi - lo) is overflowing the range of a signed integer.

> Are all GRASS modules limited to Int32, ie. -2147483648 to 214748364? I 
> can see r.mapcalc silently forces 214748364 for anything bigger...

This is not entirely correct. More findings:



The following silently forces 2147483647 on anything bigger:

$ r.mapcalc 'map=9999999999999999999'
$ r.info -rt map
min=2147483647
max=2147483647
datatype=CELL

This one too, though I'm trying to enforce double:

$ r.mapcalc 'map=double(9999999999999999999)'
$ r.info -rt map
min=2147483647.000000
max=2147483647.000000
datatype=DCELL

Trying the same by adding a decimal place separator, results in 
something bizzare to me:

$ r.mapcalc 'map=99999999999999999999999.0'
$ r.info -rt map
min=99999999999999991611392.000000
max=99999999999999991611392.000000
datatype=DCELL

$ r.mapcalc 'map=9999999999999999999.0'
$ r.info -rt map
min=10000000000000000000.000000
max=10000000000000000000.000000
datatype=DCELL


At the edges of Float32 range other strange things happen:

Shouldn't the below be rather 
min,max=340282000000000000000000000000000000000.0?:

$ r.mapcalc 'map=3.40282e38'
$ r.info -rt map
min=340282000000000014192072600942972764160.000000
max=340282000000000014192072600942972764160.000000
datatype=DCELL

The the one below should be -340282000000000000000000000000000000000.0 I 
guess:

$ r.mapcalc 'map=-3.40282e38'
$ r.info -rt map
min=-340282000000000014192072600942972764160.000000
max=-340282000000000014192072600942972764160.000000
datatype=DCEL



At bigger Float64 values r.mapcalc crashes:

$r.mapcalc 'map=3.40282e110'

*** stack smashing detected ***: r.mapcalc terminated
Aborted (core dumped)

$ r.mapcalc 'map=1.79769e+308'
  100%
*** stack smashing detected ***: r.mapcalc terminated
Aborted (core dumped

>> BTW, what are the NULL value for double and float?

Still curious (to document it).

Maciek