Dear monks and nuns,

when playing with PDL's range function I stumbled across a problem. While for dimensions up to 3 everything looks good, at d=4 something seems to be seriously broken. There is some memory corruption causing a segfault.

Looking at d=3 everything looks as expected: 

my $p = zeroes(4,4,4);
say 'p:        ', $p->info;
say 'ndcoords: ', ndcoords($p)->info;
say 'range:    ', $p->range(ndcoords($p), 2, 't')->info;

[download]

produces: 

p:        PDL: Double D [4,4,4]
ndcoords: PDL: Double D [3,4,4,4]
range:    PDL: Double D [4,4,4,2,2,2]

[download]

The first dimensions of range correspond to the second to last dimensions of the index piddle, i.e. [4,4,4]. The following dimensions correspond to the shape of the selected slices, i.e. [2,2,2].

With d=4 things become weird. 

my $q = zeroes(5,5,5,5);
say 'q:        ', $q->info;
say 'ndcoords: ', ndcoords($q)->info;
say 'range:    ', $q->range(ndcoords($q), 2, 't')->info;

[download]

produces: 

q:        PDL: Double D [5,5,5,5]
ndcoords: PDL: Double D [4,5,5,5,5]
range:    PDL: Double D [5,5,5,5,2,2,1,5]

[download]

Here we have - as expected - the second to last dimensions of the index piddle coming first. But then, instead of the expected [2,2,2,2] remainder, there comes [2,2,1,5]. Memory is corrupted afterwards, as it appears here on my Debian 11. So here is the full example script: 

#!/usr/bin/perl

use v5.24;
use warnings;
use PDL;

my $p = zeroes(4,4,4);
say 'p:        ', $p->info;
say 'ndcoords: ', ndcoords($p)->info;
say 'range:    ', $p->range(ndcoords($p), 2, 't')->info;
say ones(4);

my $q = zeroes(5,5,5,5);
say 'q:        ', $q->info;
say 'ndcoords: ', ndcoords($q)->info;
say 'range:    ', $q->range(ndcoords($q), 2, 't')->info;
say ones(5);

__DATA__
p:        PDL: Double D [4,4,4]
ndcoords: PDL: Double D [3,4,4,4]
range:    PDL: Double D [4,4,4,2,2,2]
[1 1 1 1]
q:        PDL: Double D [5,5,5,5]
ndcoords: PDL: Double D [4,5,5,5,5]
range:    PDL: Double D [5,5,5,5,2,2,1,5]
Segmentation fault

[download]

Can anybody reproduce this behaviour? If so, I'd report a bug.

Greetings,
-jo

$gryYup$d0ylprbpriprrYpkJl2xyl~rzg??P~5lp2hyl0p$

In reply to PDL range on 4-d piddles by jo37

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