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From: "Dmitry A. Kazakov" <mailbox@dmitry-kazakov.de>
Newsgroups: comp.lang.ada
Subject: Re: Efficient Sequential Access to Arrays
Date: Sun, 15 Jul 2012 21:48:35 +0200
Organization: cbb software GmbH
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Date: 2012-07-15T21:48:35+02:00
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On Sun, 15 Jul 2012 11:40:08 -0700 (PDT), Keean Schupke wrote:

> However in order to achieve this performance I needed to rework the arrays
> as the use of Indexes was too slow.

You have to measure it in order to know. Write two variants and compare
their performance.

> An example of this is lets say we are
> accessing element 5 from array A "A(5)" this requires a multiplication to
> access (base_address + index * record_size).

It does not, because 5 is constant.

> To access the neighbour A(6)
> also requires a multiplication. Accessing the array sequentially requires
> a multiplication per step. 

That depends on loop optimizations. I would expect GCC to optimize access
to array elements per the loop's index.

> So assuming we need this level of performance, what would be the best (and
> most idiomatic Ada)

Indexing is unlikely to have a significant (>5%) influence on overall
performance. Usually it is other things.

> way to package this type of usage pattern as an
> abstract datatype?

Array of aliased elements, to ensure elements independently addressable.

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