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From: dewar@merv.cs.nyu.edu (Robert Dewar)
Subject: Re: question re Ada equivalent of C function
Date: 1998/02/21
Message-ID: <dewar.888117126@merv>#1/1
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Date: 1998-02-21T00:00:00+00:00
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David Fisher says

<<Sorry if this is a bit basic, but learning Ada on one's own can be, er,
challenging.

What are the Ada equivalents of the C functions, inp and outp, used to
read a byte from or send one to a memory address?

Thanks!

David Fisher
Fisher Research Corporation
>>


First there are no such functions in the C language. They are not even
standard Unix functions, but rather some idiosyncratic library functions
from DOS-like systems.

Second, they do not read and write to/from a memory address, but rather
they access ports on DOS-like systems that allow such port access (ports
are quite different from memory addresses, since they are defined int
the IO space of the machine, rather than the memory space).

Third, if you are on one of these systems and are writing Ada, and want
to do similar highly non-portable target dependent operations, then
there are two approaches:

1. Issue the necessary In/Out instructions directly using either package
Machine code, or, preferable if your compiler supports them, machine
language intrinsics (GNAT supports both styles, see GNAT manual for
details of use).

2. Simpler probably, though less efficient, just interface to the inp and
outp routines using the usual pragma Import (C, ...) mechanism.