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Date: Mon, 07 Jul 2014 15:34:48 +0200
From: "G.B." <rm-dash-bau-haus@dash.futureapps.de>
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Subject: Re: Array slicing question
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Xref: news.eternal-september.org comp.lang.ada:20772
Date: 2014-07-07T15:34:48+02:00
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On 07.07.14 09:31, Mike Silva wrote:
> I (I being an Ada novice) am still fiddling around with writing 4 bits of LCD display data into a 32-bit GPIO register.  I have this:
>
>     type Bits_1  is mod 2**1 with Size => 1;
>     type Bits_32x1 is array (0 .. 31) of Bits_1 with Pack, Size => 32;
>     type Bits_8x1 is array (0 .. 7) of Bits_1 with Pack, Size => 8;
>
> and I want to do things like this:
>
>     a32 : Bits_32x1;
>     a8  : Bits_8x1;
> ...
>     a32(4..7) := a8(4..7);

Since this expression stays brief only as long as the slices
have no holes in them – and if atomicity of the update is
required, not touching the other bits in a32 – creating
a temporary doesn't seem so bad, perhaps hidden behind
a subprogram serving as abstraction.
   The assignment could not use a simple loop then, either,
so a bit-wise assignment from the components of a8 to components
of a32 seems still more direct than shifts and masks.

My 2¢ (for what might be too general a scheme)