Date: Mon, 22 Dec 1997 10:17:04 +0200 (IST)
From: Eli Zaretskii <eliz AT is DOT elta DOT co DOT il>
To: Dave Nugent <dave DOT nugent AT ns DOT sympatico DOT ca>
cc: djgpp AT delorie DOT com
Subject: Re: How to use _movedatal
In-Reply-To: <349D2ED7.D04@ns.sympatico.ca>
Message-ID: <Pine.SUN.3.91.971222101642.10387H-100000@is>
MIME-Version: 1.0
Content-Type: TEXT/PLAIN; charset=US-ASCII
Precedence: bulk


On Sun, 21 Dec 1997, Dave Nugent wrote:

> Hi, I'm a newbie at DJGPP, and am trying to figure out how to use
> _movedatal
> to move 32 bits at a time from one array to another.

Wrong function.  Use `memcpy' instead.  Not only is it simpler (no
segments), it is also ANSI C, so your program will be more portable to
other compilers.

> The syntax I have shows _movedata(unsigned, unsigned, unsigned,
> unsigned, size_t)
> 
> unsigned, unsigned, unsigned, unsigned WHAT?????

There's a cross-reference on that page which you were supposed to
follow.  It leads to the `movedata' page which explains all the
arguments.

> I kinda thought like unsigned src seg, unsigned src offset, unsigned
> dest seg, unsigned dest offset, but isn't DJGPP supposd to work
> without these segment headaches?

`_movedatal' is for moving data to/from portions of memory that aren't
mapped into your address space, like your SVGA's video RAM, or the
conventional memory used by DOS.  Thus you need to use a different
segment to reach them without generating a protection violation and
crashing your program.

(And btw, memory segmentation is a (mis)feature of the Intel
architecture, it doesn't go away when you switch to protected mode.)

> I would appreciate an example on how to use this.  I have a large array
> set up as follows:
> 
> long unsigned storage[1000000];
> long unsigned current[20000];
> 
> I want to be able to copy 20000 bytes from storage to current..  The
> program will determine where to start copying from in array storage.

How about this:

  #include <string.h>
  ...
  memcpy (current, storage + offset, 20000);