[Octave-bug-tracker] [bug #62968] idx_vector constructor m_len calculation is incorrect

[Maged Rifaat]

Follow-up Comment #2, bug #62968 (project octave):

[comment #1 comment #1:]
> Is `m_len` the number of elements in the idx_vector? (I think it is.) Is
`limit` included in the range? (Not sure if it is meant to be.)

Well I can't be sure in the absence of documentation, but from the usage that
I can find of this constructor across the code-base I think `limit` is not
included in the range.

For example, it was used in libinterp/corefcn/base-text-renderer line 52
<https://hg.octave.org/octave/file/tip/libinterp/corefcn/base-text-renderer.cc#l52>
for reversing a matrix like this:

idx(1) = idx_vector (pixels.dim2 ()-1, -1, -1);

Which implies that the start is included but the limit isn't, and this aligns
with the original formula (and mine).

[comment #1 comment #1:]
> Would the following change fix this?

I think your formula is very similar to the formula found in
liboctave/array/Range.h line 359
<https://hg.octave.org/octave/file/tip/liboctave/array/Range.h#l359>, but the
range class uses the same convention as Octave itself (i.e. 1:1:10 is the same
as range<double> (1, 1, 10) AFAICT), so the limit is included.


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