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From: "Dmitry A. Kazakov" <mailbox@dmitry-kazakov.de>
Newsgroups: comp.lang.ada
Subject: Re: Ada array contiguity.
Date: Sun, 19 Feb 2023 20:05:28 +0100
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On 2023-02-19 18:54, Niklas Holsti wrote:
> On 2023-02-19 17:08, Dmitry A. Kazakov wrote:

>> Rather: the bit offset of an element is a linear function of its
>> position.
> 
> That is ordering by index, but not contiguity: there may still be gaps 
> between elements. However, I assume you meant that the slope of the 
> linear function equals the component size, and then it includes contiguity.

No gaps = packed = the most dense representation.

Contiguity is rather that the gaps are regular and can be considered a 
part of each element. E.g. a video buffer with strides is not contiguous.

> The relationship of index order to memory-location order is certainly an 
> aspect that should be considered when interfacing to C or HW.

An definition of contiguous array equivalent to linearity is that the 
array body representation is isomorphic to slicing.

> Pet peeve: on more than one occasion I have been disappointed that Ada 
> representation clauses do not let me specify the index-order of packed 
> array elements in a word, relative to the bit-numbering order, and I 
> have had to fall back to using several scalar-type record components, c1 
> .. c7 say, instead of one array-type component, c(1..7).

This is as blasphemous as asking for n-D slices... (:-))

-- 
Regards,
Dmitry A. Kazakov
http://www.dmitry-kazakov.de