Re: Formal Review of std.range.ndslice

[Ilya Yaroshenko via Digitalmars-d]

On Sunday, 13 December 2015 at 21:24:36 UTC, Stefan Frijters 
wrote:
On Sunday, 13 December 2015 at 15:59:19 UTC, Ilya Yaroshenko 
wrote:
Could you please post reduced code example that caused dmd to 
segfault?

Took dustmite about 6 hours to reduce, and then I went at it 
manually for a bit, so this is the smallest I could get it:

import std.experimental.ndslice;

int main() {
  Field force;
  foreach(p, e; force) e;
}

struct Field {
  alias arr this;
  Slice!(3, double*) arr;
}

Compiled with dmd 2.069.1 via dub build:

{
    "name": "dlbc",
    "sourcePaths": ["src"],
    "dependencies": {
        "dip80-ndslice": "~>0.8.3",
    },
}

More reduced code:

import std.experimental.ndslice;

void main() {
        Slice!(3, double*) force = new double[60].sliced(3, 4, 5);

        // Correct code. Compiles!
        for(auto r = force.byElement; !r.empty; r.popFront)
        {
                size_t[3] p = r.index;
                double e = r.front;
        }

        // Wrong foreach params. dmd failed with exit code -11.
        //foreach(p, e; force)
        //{
        //}
}

dub.json
{
    "name": "dlbc",
    "dependencies": {
        "dip80-ndslice": "~>0.8.3",
    },
}

dip80-ndslice 0.8.3: target for configuration "library" is up 
to date.
dlbc ~master: building configuration "application"...
Segmentation fault
dmd failed with exit code 139.

Since it's a segfault in the compiler, should I put it on 
Bugzilla too?

Yes
1. Please note in Bugzilla report that program code is incorrect 
(see example of correct above).
2. More reduced code can be used for report:

void main() {
        Slice!(3, double*) force = new double[60].sliced(3, 4, 5);
        // Wrong foreach params. dmd failed with exit code -11.
        foreach(p, e; force)
        {
        }
}

2D way: &slice[0, 0]   or   &(slice.front.front());

ND way: &(slice.byElement.front())

Note: Comparing with unstandard  there is no guarantee that 
the first element in a ndarray is the first element in memory. 
`reversed` and `allReversed` should not be used to preserve 
strides positive.

Hm, I assumed the underlying array would be a single block of 
data and then a bunch of pointers would be used to keep track 
of any slices. I'll try to figure out how to give the data to C 
then (for MPI and HDF5, to be exact).

Probably you may need something like that:

auto ar = new double[60]; //remember ar
auto slice = ar.sliced(3, 4, 5);

However, if you have not changed slice's structure (except 
transposition), then

assert (ar == 
(&(slice.byElement.front()))[0..slice.elementsCount]);

Ilya