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From: tore@lis.pitt.edu (Tore Joergensen)
Subject: Re: GNAT Ada for DOS - Reading Integers Problem
Date: 1996/02/24
Message-ID: <4gmded$rib@toads.pgh.pa.us>#1/1
X-Deja-AN: 140878671
references: <4g2efj$d5d@susscsc1.rdg.ac.uk>
organization: University of Pittsburgh
newsgroups: comp.lang.ada
Date: 1996-02-24T00:00:00+00:00
List-Id: <comp.lang.ada>

William Paul Berriss (strberis) wrote:
[...snip...]
: What it does is this:
: When reading in the peppers.ras file it gets the nymbers form the header BUT
: instead of 512 it shows (on the screen) 131072, and instead of 24 it shows 
: something huge like 6291456.  All these 'wrong' numbers can be made from
: other numbers, e.g. 131072 is 256 times 512.  It should have been 512!

: The image is fine, I can view it on PaintBrush for windows say.
: Also, if I strip this header of 'huge' numbers and replace it with the
: numbers 512 ,512, 24, 1 etc then when I read it in again I do get the correct
: numbers, 512, 512 ,24, 1 etc.  But then, of course? , PaintBrush cannot read
: in the image. Obviously the numbers look 'funny' to IT !
[...snip...]

What you have discovered is the little endian vs. big endian problem.
You can read about it in Ada95-LRM:13.5.3. I'm not sure if gnat supports
specifying the bit_order attribute or not, but there are simple solutions
to fix it. One way to do it would be to define a 16 bit unsigned integer
and use 'A := shift_left(A,8)+shift_right(A,8);' (see LRM:B.2). I guess
somebody can tell you the best way to do it (if it isn't the above
solution).
--
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| Tore B. Joergensen      | e-mail : tore@lis.pitt.edu                |
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| 5535 Centre Avenue # 6  |                                           |
| Pgh, PA 15232, USA      | Norwegian MSIS-student at Univ. of Pgh.   |
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