[GRASS-dev] Re: r.univar: allow multiple rasters to be processed

[Ivan Shmakov]

>>>>> Glynn Clements <glynn at gclements.plus.com> writes:

 >>> I tried running r.univar on the same map for comparison, but it
 >>> crashed while trying to compute the percentile (the other
 >>> statistics were computed okay).

 >> Is it due to the memory allocation issues, or?

 > I don't know. 30m cells * 8 bytes per cell = ~240MiB. The system has
 > 1GiB of swap, so malloc() shouldn't fail.

$ nl -ba stats.c 
...
   135	    /* TODO: mode, skewness, kurtosis */
   136	    if (param.extended->answer) {
   137		qpos_perc = (int *) G_calloc(stats->n_perc, sizeof(int));
   138		quartile_perc = (double *) G_calloc(stats->n_perc, sizeof(double));
   139		for (i = 0; i < stats->n_perc; i++) {
   140		    qpos_perc[i] = (int) (stats->n * stats->perc[i] / 100. - 0.5);
   141		}
...
$ 

	Here, it should rather be, e. g.:

   qpos_perc[i] = (int) (stats->n * 1e-2 * stats->perc[i] - 0.5);

	(BTW, would it benefit from an explicit round ()?)

	Otherwise the result of the multiplication overflows the `int'
	type:

   (30 \cdot 10 ^6) \cdot 90
   \approx (2 ^5 \cdot 2 ^{20}) \cdot (2 ^6 + 2 ^5)
     > 2 ^{25} \cdot 2 ^6
       = 2 ^{31}

[...]